test(app): wait for what a timer brings, not a fixed time

CI failed on d5651c5b (run 165): the path editor's test waited 60 ms
for a save its 20 ms pause sets off, and on the runner, its CPU capped,
the timer had not fired yet. The code was the same that had passed on
the laptop.

- The path editor's test waits until the bloc has saved what was typed,
  as the step editor's test does.
- The study session's test waits until the deletion held through the
  session has gone, and the Linux Pomodoro platform's tests until the
  alert, the registration and the suggestion have come over D-Bus,
  through `eventually` (test/support), each where a fixed wait stood.
- Waits before checking that nothing happened stay as they are: a slow
  machine can only make those pass more easily.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/test/feature/study/bloc/study_session_bloc_test.dart

@@ -22,6 +22,7 @@ import 'package:halkyon_learn_flutter/src/feature/studyset/model/exam_plan.dart'
 import 'package:halkyon_learn_flutter/src/feature/studyset/model/studyset_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/tag/data/tag_repository.dart';
 
+import '../../../support/eventually.dart';
 import '../../../support/fake_card_gateway.dart';
 import '../../../support/fake_learning_path_gateway.dart';
 import '../../../support/fake_review_gateway.dart';
@@ -207,7 +208,7 @@ void main() {
 
         await bloc.close();
       });
-      await Future<void>.delayed(const Duration(milliseconds: 50));
+      await eventually(() => deletions.pending.isEmpty);
 
       expect(
         (await cards.cardsOf('japanese')).map((each) => each.content.front),