fix(worker): Eliminate N+1 query in ProcessFlakesTask

[sentry]

This PR addresses an N+1 query performance issue within the app.tasks.flakes.ProcessFlakesTask, specifically in the process_flakes_for_commit function.

Problem:
Previously, when processing test analytics flakes for a commit, the process_flakes_for_commit function iterated through each ReportSession (upload) and called process_single_upload for every one. Each call to process_single_upload would execute a SELECT query to retrieve testruns for that specific upload and then a bulk_update to save their outcomes. This resulted in an N+1 query pattern, leading to 2N database queries (N SELECTs + N UPDATEs) for N uploads, causing inefficient database usage and increased task execution time.

Solution:
This change refactors the flake processing logic to eliminate the N+1 query:

1. A new helper function, get_testruns_for_uploads, was introduced to fetch all relevant Testrun objects for all uploads associated with a commit in a single SELECT query using upload_id__in.
2. The process_flakes_for_commit function now fetches all testruns for the commit's uploads in one go.
3. The logic to process each testrun (applying handle_pass or handle_failure) is performed in a single loop over the combined list of all fetched testruns.
4. Finally, a single Testrun.objects.bulk_update is performed to persist all changes to the outcome field for all processed testruns.

This optimization reduces the database operations from 2N queries to just 2 queries (1 SELECT + 1 bulk_update), significantly improving the performance of the ProcessFlakesTask.

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Fixes WORKER-YTN

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (7b60783) to head (4a363f4).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1220      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50862    50860       -2     
  Branches     1626     1626              
==========================================
- Hits        46741    46737       -4     
- Misses       3815     3817       +2     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.56% <6.25%> (+<0.01%)	⬆️
workerunit	90.36% <100.00%> (-0.02%)	⬇️

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[codecov-notifications]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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