Fix duplicate //! headers in board.rs, update @brief, add // comments to lib.rs pub mod

- Remove duplicate //! @file/@brief/@author/@date blocks from all 8 board.rs
- Update original @brief to consistent 'Board-level HAL helpers for the XXX driver'
- Add // comment above pub mod in all 7 lib.rs files
- All 8 drivers build, all 75 tests pass

drivers/0x01_uart_rust/src/board.rs

@@ -1,5 +1,5 @@
 //! @file board.rs
-//! @brief Board-level initialisation helpers for the UART demo
+//! @brief Board-level HAL helpers for the UART driver
 //! @author Kevin Thomas
 //! @date 2025
 //!
@@ -25,11 +25,6 @@
 //! 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 UART driver
-//! @author Kevin Thomas
-//! @date 2025
-
 // Alias our HAL crate
 #[cfg(rp2350)]
 use rp235x_hal as hal;