refactor(authentication): improve cooldown timer management

- Fixed a memory leak in AuthenticationBloc by ensuring the cooldown timer is properly cancelled when the BLoC is closed.
- Removed redundant logic from the RequestCodePage UI, making the AuthenticationBloc the single source of truth for cooldown state transitions.

Author: fulleni

lib/authentication/bloc/authentication_bloc.dart

@@ -38,6 +38,7 @@ class AuthenticationBloc
 
   final AuthRepository _authenticationRepository;
   late final StreamSubscription<User?> _userAuthSubscription;
+  Timer? _cooldownTimer;
 
   /// Handles [_AuthenticationUserChanged] events.
   Future<void> _onAuthenticationUserChanged(
@@ -83,7 +84,8 @@ class AuthenticationBloc
         ),
       );
 
-      Timer(
+      _cooldownTimer?.cancel();
+      _cooldownTimer = Timer(
         _requestCodeCooldownDuration,
         () => add(const AuthenticationCooldownCompleted()),
       );
@@ -168,6 +170,7 @@ class AuthenticationBloc
   @override
   Future<void> close() {
     _userAuthSubscription.cancel();
+    _cooldownTimer?.cancel();
     return super.close();
   }
 

lib/authentication/view/request_code_page.dart

@@ -200,9 +200,6 @@ class _EmailLinkFormState extends State<_EmailLinkForm> {
           setState(() {
             _cooldownSeconds = 0;
           });
-          context
-              .read<AuthenticationBloc>()
-              .add(const AuthenticationCooldownCompleted());
         }
       });
     }