feat: Implement trip invitation functionality and notification handling

- Added TripInvitationRepository for managing trip invitations.
- Created TripInvitation model with serialization methods.
- Implemented notification payload parser for handling FCM notifications.
- Enhanced NotificationService to manage trip invitations and related actions.
- Updated UserRepository to include user search functionality.
- Modified AuthRepository to store multiple FCM tokens.
- Added tests for trip invitation logic and notification payload parsing.
- Updated pubspec.yaml and pubspec.lock for dependency management.

functions/notification_tokens.test.js

@@ -0,0 +1,24 @@
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const { extractUserFcmTokens } = require("./notification_tokens");
+
+test("extractUserFcmTokens supports legacy single token", () => {
+    const tokens = extractUserFcmTokens({ fcmToken: "token_1" });
+    assert.deepEqual(tokens, ["token_1"]);
+});
+
+test("extractUserFcmTokens merges single and multi token formats", () => {
+    const tokens = extractUserFcmTokens({
+        fcmToken: "token_legacy",
+        fcmTokens: ["token_a", "token_b"],
+    });
+    assert.deepEqual(tokens, ["token_legacy", "token_a", "token_b"]);
+});
+
+test("extractUserFcmTokens filters invalid values", () => {
+    const tokens = extractUserFcmTokens({
+        fcmToken: "",
+        fcmTokens: ["valid", null, 42, ""],
+    });
+    assert.deepEqual(tokens, ["valid"]);
+});