refactor: enforce max 8 code lines, add docstrings, fix warnings across all Rust and C SDK projects

Rust (all 15 projects):
- Refactored overlength functions: format_counter, format_u8, format_f32_1,
  format_u32_minimal, gpio_drive, read_sensor, poll_sensor, format_round_trip,
  format_u32, prepare_write_buf, write_min_digits, write_temp, UartDriver::init,
  init_spi, angle_to_pulse_us, compute_servo_level
- Added 200+ docstrings to test functions, mock structs, impl blocks
- Fixed pub static comments (//) to doc comments (///) in all main.rs files
- Fixed helper function ordering (helpers above callers)
- Fixed Fn(u32) -> FnMut(u32) bound in button poll_button
- Moved OneShot trait import from main.rs to board.rs in adc project
- Added unsafe {} blocks in flash unsafe fn bodies (Rust 2024 edition)
- Removed unused hal::Clock imports from pwm/servo main.rs
- All 15 projects build with zero errors and zero warnings

C Pico SDK (all 15 projects):
- Added docstrings to all public functions, macros, and static variables
- All 15 projects rebuilt with zero errors

Cleanup:
- Removed build/ and target/ directories from git tracking
- Added target/ to .gitignore
- Deleted temporary fix_rust_docs.py script

drivers/0x03_button_cbm/Inc/rp2350_reset_handler.h

@@ -6,7 +6,7 @@
   *
   *          Entry point after reset. Performs stack initialization, XOSC
   *          setup, subsystem reset release, UART initialization,
-  *          coprocessor enable, and branches to main().
+  *          and branches to main().
   *
   ******************************************************************************
   * @attention

drivers/0x03_button_cbm/Src/rp2350_button.c

@@ -38,12 +38,23 @@ static bool _debounce_confirm(uint32_t pin)
   return !gpio_get(pin);
 }
 
+/**
+  * @brief  Initialize a GPIO pin as an active-low button input with pull-up.
+  * @param  pin         GPIO pin number to configure as a button input
+  * @param  debounce_ms debounce settling time in milliseconds
+  * @retval None
+  */
 void button_init(uint32_t pin, uint32_t debounce_ms)
 {
   debounce_delay_ms = debounce_ms;
   gpio_config_input_pullup(pin);
 }
 
+/**
+  * @brief  Read the debounced state of the button.
+  * @param  pin GPIO pin number previously initialized with button_init()
+  * @retval bool true if the button is firmly pressed, false if released
+  */
 bool button_is_pressed(uint32_t pin)
 {
   if (!gpio_get(pin))

drivers/0x03_button_cbm/Src/rp2350_delay.c

@@ -22,6 +22,11 @@
 
 #include "rp2350_delay.h"
 
+/**
+  * @brief  Delay for the specified number of milliseconds.
+  * @param  ms number of milliseconds to delay
+  * @retval None
+  */
 void delay_ms(uint32_t ms)
 {
   if (ms == 0)

drivers/0x03_button_cbm/Src/rp2350_gpio.c

@@ -78,6 +78,11 @@ static void _gpio_enable_output(uint32_t gpio_num)
   SIO[SIO_GPIO_OE_SET_OFFSET] = (1U << gpio_num);
 }
 
+/**
+  * @brief  Configure a GPIO pin as SIO output.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
 void gpio_config(uint32_t gpio_num)
 {
   _gpio_config_pad(gpio_num);
@@ -85,26 +90,51 @@ void gpio_config(uint32_t gpio_num)
   _gpio_enable_output(gpio_num);
 }
 
+/**
+  * @brief  Drive a GPIO output high.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
 void gpio_set(uint32_t gpio_num)
 {
   SIO[SIO_GPIO_OUT_SET_OFFSET] = (1U << gpio_num);
 }
 
+/**
+  * @brief  Drive a GPIO output low.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
 void gpio_clear(uint32_t gpio_num)
 {
   SIO[SIO_GPIO_OUT_CLR_OFFSET] = (1U << gpio_num);
 }
 
+/**
+  * @brief  Toggle a GPIO output.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
 void gpio_toggle(uint32_t gpio_num)
 {
   SIO[SIO_GPIO_OUT_XOR_OFFSET] = (1U << gpio_num);
 }
 
+/**
+  * @brief  Read the current input level of a GPIO pin.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval bool true if pin is high, false if low
+  */
 bool gpio_get(uint32_t gpio_num)
 {
   return (SIO[SIO_GPIO_IN_OFFSET] & (1U << gpio_num)) != 0;
 }
 
+/**
+  * @brief  Configure a GPIO pin as SIO input with internal pull-up.
+  * @param  gpio_num GPIO pin number (0-29)
+  * @retval None
+  */
 void gpio_config_input_pullup(uint32_t gpio_num)
 {
   _gpio_config_pad_input_pullup(gpio_num);

drivers/0x03_button_cbm/Src/rp2350_led.c

@@ -22,27 +22,52 @@
 #include "rp2350_led.h"
 #include "rp2350_gpio.h"
 
+/**
+  * @brief  Initialize a GPIO pin as a push-pull digital output.
+  * @param  pin GPIO pin number to configure
+  * @retval None
+  */
 void led_init(uint32_t pin)
 {
   gpio_config(pin);
   gpio_clear(pin);
 }
 
+/**
+  * @brief  Drive the output pin high (LED on).
+  * @param  pin GPIO pin number
+  * @retval None
+  */
 void led_on(uint32_t pin)
 {
   gpio_set(pin);
 }
 
+/**
+  * @brief  Drive the output pin low (LED off).
+  * @param  pin GPIO pin number
+  * @retval None
+  */
 void led_off(uint32_t pin)
 {
   gpio_clear(pin);
 }
 
+/**
+  * @brief  Toggle the current state of the output pin.
+  * @param  pin GPIO pin number
+  * @retval None
+  */
 void led_toggle(uint32_t pin)
 {
   gpio_toggle(pin);
 }
 
+/**
+  * @brief  Query the current drive state of the output pin.
+  * @param  pin GPIO pin number
+  * @retval bool true if the pin is driven high, false if low
+  */
 bool led_get_state(uint32_t pin)
 {
   return gpio_get(pin);

drivers/0x03_button_cbm/Src/rp2350_reset.c

@@ -22,6 +22,10 @@
 
 #include "rp2350_reset.h"
 
+/**
+  * @brief  Release IO_BANK0 from reset and wait until ready.
+  * @retval None
+  */
 void reset_init_subsystem(void)
 {
   uint32_t value;

drivers/0x03_button_cbm/Src/rp2350_reset_handler.c

@@ -29,6 +29,10 @@
 
 extern int main(void);
 
+/**
+  * @brief  Reset handler entry point (naked, noreturn).
+  * @retval None
+  */
 void __attribute__((naked, noreturn)) Reset_Handler(void)
 {
   __asm__ volatile (

drivers/0x03_button_cbm/Src/rp2350_stack.c

@@ -21,6 +21,10 @@
 
 #include "rp2350_stack.h"
 
+/**
+  * @brief  Initialize MSP, PSP, MSPLIM, and PSPLIM stack pointers.
+  * @retval None
+  */
 void stack_init(void)
 {
   __asm__ volatile (

drivers/0x03_button_cbm/Src/rp2350_uart.c

@@ -79,12 +79,20 @@ static void _uart_enable(void)
   UART_BASE[UART_CR_OFFSET] = UART_CR_ENABLE;
 }
 
+/**
+  * @brief  Release UART0 from reset and wait until ready.
+  * @retval None
+  */
 void uart_release_reset(void)
 {
   _uart_clear_reset_bit();
   _uart_wait_reset_done();
 }
 
+/**
+  * @brief  Initialize UART0 pins, baud rate, line control, and enable.
+  * @retval None
+  */
 void uart_init(void)
 {
   _uart_configure_pins();
@@ -92,11 +100,19 @@ void uart_init(void)
   _uart_enable();
 }
 
+/**
+  * @brief  Check whether a received byte is waiting in the UART FIFO.
+  * @retval bool true if at least one byte is available
+  */
 bool uart_is_readable(void)
 {
   return (UART_BASE[UART_FR_OFFSET] & UART_FR_RXFE_MASK) == 0;
 }
 
+/**
+  * @brief  Read one character from UART0 (blocking).
+  * @retval char the received character
+  */
 char uart_getchar(void)
 {
   while (UART_BASE[UART_FR_OFFSET] & UART_FR_RXFE_MASK) {
@@ -104,6 +120,11 @@ char uart_getchar(void)
   return (char)(UART_BASE[UART_DR_OFFSET] & 0xFF);
 }
 
+/**
+  * @brief  Transmit one character over UART0 (blocking).
+  * @param  c character to transmit
+  * @retval None
+  */
 void uart_putchar(char c)
 {
   while (UART_BASE[UART_FR_OFFSET] & UART_FR_TXFF_MASK) {
@@ -111,6 +132,11 @@ void uart_putchar(char c)
   UART_BASE[UART_DR_OFFSET] = (uint32_t)c;
 }
 
+/**
+  * @brief  Transmit a null-terminated string over UART0.
+  * @param  str pointer to the string to send
+  * @retval None
+  */
 void uart_puts(const char *str)
 {
   while (*str) {
@@ -118,6 +144,11 @@ void uart_puts(const char *str)
   }
 }
 
+/**
+  * @brief  Convert a lowercase ASCII character to uppercase.
+  * @param  c input character
+  * @retval char uppercase equivalent or original character
+  */
 char uart_to_upper(char c)
 {
   if (c >= 'a' && c <= 'z')

drivers/0x03_button_cbm/Src/rp2350_xosc.c

@@ -22,6 +22,10 @@
 
 #include "rp2350_xosc.h"
 
+/**
+  * @brief  Initialize the external crystal oscillator and wait until stable.
+  * @retval None
+  */
 void xosc_init(void)
 {
   XOSC->STARTUP = 0x00C4U;
@@ -30,6 +34,10 @@ void xosc_init(void)
   }
 }
 
+/**
+  * @brief  Enable the XOSC peripheral clock via CLK_PERI_CTRL.
+  * @retval None
+  */
 void xosc_enable_peri_clk(void)
 {
   uint32_t value;