Add inline // comments to all main.rs and board.rs boilerplate across 0x01-0x08 Rust drivers

- Add // comments to mod declarations, use imports, static items, and
  PICOTOOL_ENTRIES in all 8 main.rs files matching rp-hal template style
- Add //! file headers to all 8 board.rs files
- Add // comments to all board.rs use imports and HAL alias
- All 8 drivers build successfully, all 75 tests pass

drivers/0x03_button_rust/src/board.rs

@@ -25,14 +25,23 @@
 //! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 //! SOFTWARE.
 
+//! @file board.rs
+//! @brief Board-level HAL helpers for the button driver
+//! @author Kevin Thomas
+//! @date 2025
+
+// Rate extension trait for .Hz() baud rate construction
 use fugit::RateExtU32;
+// Clock trait for accessing system clock frequency
 use hal::Clock;
+// GPIO pin types and function selectors
 use hal::gpio::{FunctionNull, FunctionUart, Pin, PullDown, PullNone};
+// UART configuration and peripheral types
 use hal::uart::{DataBits, Enabled, StopBits, UartConfig, UartPeripheral};
 
+// Alias our HAL crate
 #[cfg(rp2350)]
 use rp235x_hal as hal;
-
 #[cfg(rp2040)]
 use rp2040_hal as hal;