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

[sentry]

This PR addresses an N+1 query performance issue within the app.tasks.flakes.ProcessFlakesTask.

Problem:
Previously, the process_flakes_for_commit function iterated through each ReportSession (upload) and, for every upload, made a separate database query to fetch its associated Testrun objects via get_testruns(upload). This resulted in N+1 queries, where N is the number of uploads, leading to inefficient database usage.

Solution:

1. Introduced get_testruns_for_uploads to fetch all relevant Testrun objects for all uploads in a single batched query using upload_id__in.
2. The fetched Testrun objects are then grouped by upload_id in Python.
3. The process_single_upload function was modified to accept a pre-fetched list of Testrun objects, eliminating its internal database call.
4. process_flakes_for_commit now calls the batch fetch function once and passes the appropriate subset of Testrun objects to process_single_upload for each iteration.

This change significantly reduces the number of database queries, improving the performance of the ProcessFlakesTask.

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Fixes WORKER-YYJ

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.88%. Comparing base (701e991) to head (0be0c03).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...orker/services/test_analytics/ta_process_flakes.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1411      +/-   ##
==========================================
- Coverage   91.89%   91.88%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50868    50877       +9     
  Branches     1626     1626              
==========================================
+ Hits        46744    46750       +6     
- Misses       3818     3821       +3     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.53% <8.33%> (-0.03%)	⬇️
workerunit	90.36% <91.66%> (-0.02%)	⬇️

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Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...orker/services/test_analytics/ta_process_flakes.py	91.66%	1 Missing ⚠️

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