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

[sentry]

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

Problem: Previously, when processing flakes for a commit with multiple associated uploads, the process_single_upload function was called for each upload. Inside this function, a SELECT query was executed to fetch testruns for that specific upload, followed by a bulk_update for those testruns. This resulted in 2*N database queries (N SELECTs + N UPDATEs), where N is the number of uploads for a commit.

Solution:

1. Introduced get_testruns_for_uploads to fetch all relevant testruns for all uploads of a commit in a single batched SELECT query.
2. Refactored process_single_upload to accept a pre-fetched list of testruns, removing its internal database query.
3. Modified process_flakes_for_commit to collect all mutated Testrun objects across all uploads and perform a single Testrun.objects.bulk_update after iterating through all uploads.

This change reduces the database interaction from 2*N queries to just 2 queries (one batched SELECT and one batched UPDATE) for the ta_timeseries_testrun table, significantly improving performance for commits with many uploads.

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Fixes WORKER-YYW

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (701e991) to head (6810c94).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1425   +/-   ##
=======================================
  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	58.53% <7.14%> (-0.04%)	⬇️
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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