fix(worker): optimize ProcessFlakesTask N+1 query

[sentry]

The ProcessFlakesTask was suffering from an N+1 query issue in apps/worker/services/test_analytics/ta_process_flakes.py.
Specifically, the process_flakes_for_commit function iterated over uploads, and for each upload, it called process_single_upload, which in turn called get_testruns(upload). This resulted in a separate database query for testruns for each upload, leading to N+1 queries.

This change refactors the flake processing to:

1. Introduce get_all_testruns to fetch all relevant testruns for all uploads in a single database query.
2. Modify process_single_upload to accept a pre-fetched list of testruns, eliminating its internal database query.
3. Accumulate all modified testruns and perform a single Testrun.objects.bulk_update after processing all uploads, instead of multiple individual updates.

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

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Fixes WORKER-YV9

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (e682d07) to head (d6588f3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1239      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50868    50878      +10     
  Branches     1626     1626              
==========================================
+ Hits        46744    46752       +8     
- Misses       3818     3820       +2     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.53% <7.14%> (-0.04%)	⬇️
workerunit	90.36% <100.00%> (-0.01%)	⬇️

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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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