fix(test): pty_log_test imports package:test, not flutter_test

The breadcrumb unit test (T-434) pulled package:flutter_test, which imports
dart:ui — unavailable under plain `dart test`. That broke the flutter-free
core batch (ci/test_core.sh) for every file compiled after it. It uses only
package:test APIs, so the import was simply wrong; siblings already use
package:test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/pty/pty_log_test.dart

@@ -3,7 +3,7 @@
 import 'dart:io';
 
 import 'package:clide/src/pty/pty_log.dart';
-import 'package:flutter_test/flutter_test.dart';
+import 'package:test/test.dart';
 
 void main() {
   group('PtyLog', () {