refactor: LoRaBoard trait with full associated types + BoardParts

- LoRaBoard trait now has associated types: RadioParts, CommParts, DisplayParts, DisplayDriver
- into_parts() is on the trait (enforced by compiler, not implicit convention)
- BoardParts<R, C, D> struct replaces tuple return from into_parts()
- mac_address() stays on trait, MAC also in BoardParts for convenience
- Removed mac field from DisplayParts (display task calls Board::mac_address())
- DisplayDriver associated type requires DrawTarget<Color = BinaryColor>

firmware/src/display.rs

@@ -108,7 +108,7 @@ pub async fn display_task(
 ) {
     // Format MAC address as "XX:XX:XX:XX:XX:XX"
     let mut mac_str: heapless::String<18> = heapless::String::new();
-    let m = parts.mac;
+    let m = Board::mac_address();
     let _ = core::fmt::Write::write_fmt(
         &mut mac_str,
         format_args!(