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/0x0d_timer_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/0x0d_timer_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)
@@ -38,6 +43,11 @@ void delay_ms(uint32_t ms)
   );
 }
 
+/**
+  * @brief  Delay for the specified number of microseconds.
+  * @param  us number of microseconds to delay
+  * @retval None
+  */
 void delay_us(uint32_t us)
 {
   if (us == 0)

drivers/0x0d_timer_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/0x0d_timer_cbm/Src/rp2350_reset_handler.c

@@ -40,6 +40,10 @@ void _late_init(void)
   timer_tick_init();
 }
 
+/**
+  * @brief  Reset handler entry point (naked, noreturn).
+  * @retval None
+  */
 void __attribute__((naked, noreturn)) Reset_Handler(void)
 {
   __asm__ volatile (

drivers/0x0d_timer_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/0x0d_timer_cbm/Src/rp2350_timer.c

@@ -102,18 +102,32 @@ static void _timer_arm_alarm(void)
   TIMER0->ALARM0 = target;
 }
 
+/**
+  * @brief  Release TIMER0 from reset and wait until ready.
+  * @retval None
+  */
 void timer_release_reset(void)
 {
   _timer_clear_reset_bit();
   _timer_wait_reset_done();
 }
 
+/**
+  * @brief  Start the TIMER0 tick generator at 1 us resolution.
+  * @retval None
+  */
 void timer_tick_init(void)
 {
   _timer_set_tick_cycles();
   _timer_enable_tick();
 }
 
+/**
+  * @brief  Start a repeating alarm that fires every period_ms milliseconds.
+  * @param  period_ms interval in milliseconds between callbacks
+  * @param  cb        function to call on each alarm
+  * @retval None
+  */
 void timer_alarm_start(uint32_t period_ms, timer_callback_t cb)
 {
   _user_callback = cb;

drivers/0x0d_timer_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/0x0d_timer_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;
@@ -40,6 +48,10 @@ void xosc_enable_peri_clk(void)
   CLOCKS->CLK_PERI_CTRL = value;
 }
 
+/**
+  * @brief  Switch CLK_REF source to XOSC for a stable 12 MHz clk_sys.
+  * @retval None
+  */
 void xosc_set_clk_ref(void)
 {
   CLOCKS->CLK_REF_CTRL = CLK_REF_CTRL_SRC_XOSC;