Stop using remaining_jobs and failed_jobs and use jobs statuses instead

[ievdokdm]

Remove remaining_jobs and failed_jobs from presubmit_guards

Remove the remaining_jobs and failed_jobs fields from PresubmitGuard and derive guard status directly from the jobs TaskStatus map instead of maintaining separate counters.

• Update GuardStatus.calculate to evaluate Iterable (Succeeded if all isSuccess, Failed if any isFailure, otherwise In Progress)
• Add PresubmitGuard.status getter and drop remainingJobs/failedJobs
• Update UnifiedCheckRun, LuciBuildService, request handlers, and unit tests

fix: flutter/flutter#193862

[gemini-code-assist]

Code Review

This pull request refactors the PresubmitGuard and GuardStatus logic to eliminate the redundant tracking of remainingJobs and failedJobs counters, opting instead to dynamically calculate the guard status directly from the individual job statuses. Numerous request handlers, services, and tests have been updated to support this simplified approach. Additionally, three new users were added to the resetFailedCheckRun configuration. No review comments were provided, so there is no feedback to address.