fix: smooth scan RSSI readings

test/controller/bluetooth_test.dart

@@ -0,0 +1,70 @@
+import 'package:abawo_bt_app/controller/bluetooth.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('RssiAverager', () {
+    test('averages samples within the configured window', () {
+      final averager = RssiAverager(window: const Duration(milliseconds: 500));
+      final startedAt = DateTime(2026);
+
+      expect(averager.addSample('trainer', -80, startedAt), -80);
+      expect(
+        averager.addSample(
+          'trainer',
+          -70,
+          startedAt.add(const Duration(milliseconds: 100)),
+        ),
+        -75,
+      );
+      expect(
+        averager.addSample(
+          'trainer',
+          -60,
+          startedAt.add(const Duration(milliseconds: 400)),
+        ),
+        -70,
+      );
+    });
+
+    test('drops samples older than the configured window', () {
+      final averager = RssiAverager(window: const Duration(milliseconds: 500));
+      final startedAt = DateTime(2026);
+
+      averager.addSample('trainer', -80, startedAt);
+      averager.addSample(
+        'trainer',
+        -60,
+        startedAt.add(const Duration(milliseconds: 250)),
+      );
+
+      expect(
+        averager.addSample(
+          'trainer',
+          -40,
+          startedAt.add(const Duration(milliseconds: 501)),
+        ),
+        -50,
+      );
+    });
+
+    test('tracks devices independently', () {
+      final averager = RssiAverager(window: const Duration(milliseconds: 500));
+      final startedAt = DateTime(2026);
+
+      averager.addSample('trainer-a', -80, startedAt);
+      averager.addSample('trainer-a', -60, startedAt);
+
+      expect(averager.addSample('trainer-b', -40, startedAt), -40);
+    });
+
+    test('clear removes previous samples', () {
+      final averager = RssiAverager(window: const Duration(milliseconds: 500));
+      final startedAt = DateTime(2026);
+
+      averager.addSample('trainer', -80, startedAt);
+      averager.clear();
+
+      expect(averager.addSample('trainer', -40, startedAt), -40);
+    });
+  });
+}