Exercise: Log exercise answer changes without affecting scores - refs #6225

[christianbeeznest]

Implemented exercise answer history tracking for both Vue and legacy saving flows.

Added a new track_e_attempt_log table to preserve answer changes without affecting existing answers or grading.

Validated the migration, PHPUnit tests, frontend build, and a completed exercise attempt with a score of 20/30.

The database migration must be executed after deployment.

[codecov]

Codecov Report

❌ Patch coverage is 49.53271% with 54 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.22%. Comparing base (2b9532f) to head (6eef810).
⚠️ Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
.../State/Exercise/ExerciseRuntimeAnswerProcessor.php	0.00%	33 Missing ⚠️
...e/Migrations/Schema/V310/Version20261019213000.php	22.22%	7 Missing ⚠️
.../Exercise/ExerciseRuntimeUploadAnswerProcessor.php	0.00%	6 Missing ⚠️
src/CoreBundle/Entity/TrackEAttemptLog.php	87.09%	4 Missing ⚠️
...dle/Service/Exercise/ExerciseAttemptLogService.php	85.71%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #9277      +/-   ##
============================================
+ Coverage     17.20%   17.22%   +0.01%     
- Complexity    62176    62207      +31     
============================================
  Files          2522     2525       +3     
  Lines        233319   233426     +107     
============================================
+ Hits          40150    40215      +65     
- Misses       193169   193211      +42     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.