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

[sentry]

This PR addresses an N+1 query issue identified in app.tasks.flakes.ProcessFlakesTask, specifically within the process_flakes_for_commit function in apps/worker/services/test_analytics/ta_process_flakes.py.

Problem:
Previously, when processing flakes for a commit, the process_flakes_for_commit function would iterate over each ReportSession (upload). For each upload, it would call process_single_upload, which in turn performed a separate SELECT query to fetch testruns and a bulk_update operation on Testrun objects. This led to an O(2N) query pattern, where N is the number of uploads for a given commit.

Solution:

1. Batch-fetch Testruns: Introduced get_testruns_for_uploads to fetch all relevant Testrun objects for all uploads associated with a commit in a single SELECT query. The results are grouped by upload_id for efficient lookup.
2. Refactored process_single_upload: Modified process_single_upload to accept the pre-fetched list of Testrun objects directly, eliminating its internal database query.
3. Single Bulk Update: All modified Testrun objects across all uploads are now collected into a single list. A single Testrun.objects.bulk_update call is performed after the loop, updating all outcomes in one go.

Impact:
This change reduces the database query count from O(2N) to O(2) per commit, significantly improving performance and reducing database load when processing test analytics flakes.

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Fixes WORKER-YYG

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (701e991) to head (9d6323d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1409   +/-   ##
=======================================
  Coverage   91.89%   91.89%           
=======================================
  Files        1325     1325           
  Lines       50868    50875    +7     
  Branches     1626     1626           
=======================================
+ Hits        46744    46751    +7     
  Misses       3818     3818           
  Partials      306      306           

Flag	Coverage Δ
workerintegration	58.54% <7.14%> (-0.03%)	⬇️
workerunit	90.38% <100.00%> (+<0.01%)	⬆️

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Codecov Report

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

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