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

[sentry]

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

Problem: The process_flakes_for_commit function iterated through ReportSession uploads and, for each upload, executed a separate database query to fetch associated Testrun objects via get_testruns. This resulted in an N+1 query pattern, where N is the number of uploads for a given commit.

Solution:

1. A new function, get_testruns_for_uploads, was introduced to fetch all relevant Testrun objects for a list of ReportSession uploads in a single batched query using upload_id__in.
2. The results are then grouped by upload_id into a dictionary.
3. process_flakes_for_commit now calls this new batch-fetching function once, and passes the pre-fetched and grouped Testrun objects to process_single_upload.
4. process_single_upload was updated to accept these pre-fetched testruns, avoiding individual database calls within the loop.

This change significantly reduces the number of database queries from 1 + N to 2 (one for uploads, one for all testruns), improving the performance of the ProcessFlakesTask.

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Fixes WORKER-YYS

[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 (d2c66f3).
✅ 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    #1421      +/-   ##
==========================================
- 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-notifications]

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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