183602 Fix an issue with updating proper job attempt numbers on re-run

[ievdokdm]

1. Refactored Pull Request Retrieval

• Updated Handlers: The logic in rerun_all_failed_jobs.dart and rerun_failed_job.dart has been updated to consistently use PrCheckRuns.findPullRequestFor to resolve the pull request via the commit SHA (guard.commitSha), rather than querying by PR number.
• Fixed Re-run Workflows: Ensured that the handlers fetch the correct active pull request during re-runs and store the proper retry number/attempt information when invoking reScheduleTryBuilds.

2. Removed pull_request_num Field and Cache

• Model Cleanups: The pull_request_num field was entirely removed from the PrCheckRuns Firestore model, including its related mappings and integration test matchers (_pr_check_run.dart).
• Removed Methods: Deleted the obsolete findPullRequestCachedForPullRequestNum lookup method from both PrCheckRuns and the Scheduler service. Additionally, removed its related caching tests.

3. Service/Dependencies Cleanup

• Removed Unused Services: Dropped the previously injected but unused _githubService from scheduler.dart.
• Code Formatting: Ran standard Dart formatting rules (dart format) to ensure code uniformity in edited files.

4. Test Suite Adjustments

• Updated Mocks & Setup: rerun_all_failed_jobs_test.dart and rerun_failed_job_test.dart were updated to properly seed data using PrCheckRuns.initializeDocument(...) mirroring production behavior.
• Updated Assertions: Test assertions were updated to verify correct PR handling, most notably checking that reScheduleTryBuilds receives accurate target configurations (e.g., proper attempt increments like containsPair(targetA, 2)).
• Removed Deprecated Mocks: Scrubbed generated files like mocks.mocks.dart and testing data_seeder.dart to remove references to the deleted fields and getters.

fix: flutter/flutter#183602

[github-actions]

🤖 Hi @ievdokdm, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[github-actions]

## 📋 Review Summary

This Pull Request removes the caching functionality for pull requests by number from the Scheduler and relies instead on finding the pull request by SHA from Firestore in the API handlers for rerunning jobs. While the code changes align with simplifying the caching logic, they introduce a logical flaw related to how pull requests are queried.

🔍 General Feedback

• The refactoring nicely cleans up the API handlers by unifying the logic used for rerunning failed jobs.
• Removing pullRequestNum and relying solely on the SHA to fetch PRs introduces a potential conflict since a single SHA can be associated with multiple Pull Requests.
• Please consider retaining the PR number lookup to ensure the API precisely operates on the intended pull request context.

[auto-submit]

auto label is removed for flutter/cocoon/4988, Failed to merge flutter/cocoon/4988 with Pull request flutter/cocoon/4988 could not be merged: Required status check "ci.yaml validation" is expected..

[auto-submit]

auto label is removed for flutter/cocoon/4988, Failed to merge flutter/cocoon/4988 with Pull request flutter/cocoon/4988 could not be merged: Required status check "ci.yaml validation" is expected..