Add requestConnectionPriority support (#221)

* feat: add requestConnectionPriority

- Add BleConnectionPriority enum (balanced, highPerformance, lowPower)
- Add BleCapabilities.supportsConnectionPriorityApi flag
- Implement on Android via BluetoothGatt.requestConnectionPriority()
- Throw notSupported on iOS, macOS, Windows, Linux, and Web
- Update pigeon definition and regenerate platform channel files
- Bump version 1.2.0 -> 1.3.0

* fix: improve requestConnectionPriority implementation

- Remove redundant BleCapabilities guard in Dart layer (native handles it)
- Add BleConnectionPriority Kotlin enum mirroring Dart enum
- Map to explicit Android SDK constants via when expression
- Add firstOrNull with ILLEGAL_ARGUMENT for unknown priority values
- Add catch (e: Exception) block for broader error handling
- Fix enum doc comment (throws belongs on method, not enum)
- Remove stale capability check guidance from docs and README

---------

Co-authored-by: aqeel-bmec-co <aqeel@bmec.co>
Co-authored-by: aqeel-bmec-co <85945830+aqeel-bmec-co@users.noreply.github.com>

example/lib/data/mock_universal_ble.dart

@@ -103,6 +103,12 @@ class MockUniversalBle extends UniversalBlePlatform {
     return 512;
   }
 
+  @override
+  Future<void> requestConnectionPriority(
+    String deviceId,
+    BleConnectionPriority priority,
+  ) async {}
+
   @override
   Future<void> setNotifiable(String deviceId, String service,
       String characteristic, BleInputProperty bleInputProperty) async {}