Implement readRSSI on Android and Darwin (#203)

example/lib/data/mock_universal_ble.dart

@@ -113,6 +113,12 @@ class MockUniversalBle extends UniversalBlePlatform {
     return 512;
   }
 
+  @override
+  Future<int> readRssi(String deviceId) async {
+    await Future.delayed(const Duration(milliseconds: 500));
+    return -50; // Mock RSSI value in dBm
+  }
+
   @override
   Future<void> setNotifiable(String deviceId, String service,
       String characteristic, BleInputProperty bleInputProperty) async {}

example/lib/peripheral_details/peripheral_detail_page.dart

@@ -1097,6 +1097,30 @@ class _PeripheralDetailPageState extends State<PeripheralDetailPage> {
                         ),
                       ),
                     ),
+                    OutlinedButton.icon(
+                      onPressed: isConnected
+                          ? () async {
+                              try {
+                                int rssi = await bleDevice.readRssi();
+                                _addLog('RSSI', '$rssi dBm');
+                              } catch (e) {
+                                _addLog('ReadRssiError (${e.runtimeType})', e);
+                              }
+                            }
+                          : null,
+                      icon: const Icon(Icons.signal_cellular_alt),
+                      label: const Text('Get RSSI'),
+                      style: OutlinedButton.styleFrom(
+                        foregroundColor: colorScheme.onSurface,
+                        padding: const EdgeInsets.symmetric(
+                          horizontal: 16,
+                          vertical: 12,
+                        ),
+                        shape: RoundedRectangleBorder(
+                          borderRadius: BorderRadius.circular(8),
+                        ),
+                      ),
+                    ),
                     if (BleCapabilities.supportsRequestMtuApi)
                       ElevatedButton.icon(
                         onPressed: isConnected