Add transmission timing details

test/models/message_reception_details_test.dart

@@ -0,0 +1,27 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meshcore_sar_app/models/message_reception_details.dart';
+
+void main() {
+  test('round trips reception details json', () {
+    final details = MessageReceptionDetails(
+      capturedAt: DateTime.fromMillisecondsSinceEpoch(1700000000000),
+      packetLoggedAt: DateTime.fromMillisecondsSinceEpoch(1700000000500),
+      rssiDbm: -92,
+      snrDb: 7.5,
+      pathBytes: const [0xAA, 0xBB, 0xCC],
+      senderToReceiptMs: 4200,
+      estimatedTransmitMs: 1800,
+      postTransmitDelayMs: 2400,
+    );
+
+    final decoded = MessageReceptionDetails.fromJson(details.toJson());
+
+    expect(decoded, isNotNull);
+    expect(decoded!.rssiDbm, -92);
+    expect(decoded.snrDb, 7.5);
+    expect(decoded.pathBytesHex, 'aa:bb:cc');
+    expect(decoded.senderToReceiptMs, 4200);
+    expect(decoded.estimatedTransmitMs, 1800);
+    expect(decoded.postTransmitDelayMs, 2400);
+  });
+}