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/0x01_uart/uart.c

@@ -32,32 +32,66 @@
 #include "hardware/uart.h"
 #include "hardware/gpio.h"
 
+/** @brief Hardware UART instance used by this driver */
 #define UART_INST uart0
 
+/**
+ * @brief Initialize hardware UART0 on the specified TX and RX GPIO pins
+ *
+ * @param tx_pin   GPIO pin number to use as UART0 TX
+ * @param rx_pin   GPIO pin number to use as UART0 RX
+ * @param baud_rate Desired baud rate in bits per second
+ */
 void uart_driver_init(uint32_t tx_pin, uint32_t rx_pin, uint32_t baud_rate) {
     uart_init(UART_INST, baud_rate);
     gpio_set_function(tx_pin, GPIO_FUNC_UART);
     gpio_set_function(rx_pin, GPIO_FUNC_UART);
 }
 
+/**
+ * @brief Check whether a received character is waiting in the UART FIFO
+ *
+ * @return bool true if at least one byte is available to read
+ */
 bool uart_driver_is_readable(void) {
     return uart_is_readable(UART_INST);
 }
 
+/**
+ * @brief Read one character from UART0 (blocking)
+ *
+ * @return char The received character
+ */
 char uart_driver_getchar(void) {
     return (char)uart_getc(UART_INST);
 }
 
+/**
+ * @brief Transmit one character over UART0 (blocking)
+ *
+ * @param c Character to transmit
+ */
 void uart_driver_putchar(char c) {
     uart_putc_raw(UART_INST, c);
 }
 
+/**
+ * @brief Transmit a null-terminated string over UART0
+ *
+ * @param str Pointer to the string to transmit
+ */
 void uart_driver_puts(const char *str) {
     while (*str) {
         uart_putc_raw(UART_INST, *str++);
     }
 }
 
+/**
+ * @brief Convert a character to uppercase
+ *
+ * @param c Character to convert
+ * @return char Uppercase version if 'a'-'z', otherwise unchanged
+ */
 char uart_driver_to_upper(char c) {
     if (c >= 'a' && c <= 'z') {
         return (char)(c - 32);