perf(worker): Optimize N+1 queries in ProcessFlakesTask

[sentry]

This PR addresses the N+1 query issue (WORKER-YTD) identified in app.tasks.flakes.ProcessFlakesTask within apps/worker/services/test_analytics/ta_process_flakes.py.

Problem:
Previously, the process_flakes_for_commit function iterated over each upload, leading to:

1. A separate database query for Testrun objects for each upload (get_testruns(upload)).
2. A separate Testrun.objects.bulk_update call for each upload.
3. Individual flake.save() calls when a flake expired.
   This resulted in an N+1 query pattern, causing excessive database load and slower processing times proportional to the number of uploads.

Solution:
This change refactors the flake processing logic to batch database operations:

1. Batch Testrun Fetch: Introduced get_testruns_for_uploads to fetch all relevant Testrun objects for all uploads in a single query, then groups them by upload_id.
2. Refactored process_single_upload: Modified to accept pre-fetched Testrun objects and an expired_flakes list, removing internal DB queries and individual bulk_update calls.
3. Consolidated Testrun Updates: All modified Testrun objects from all uploads are now collected and updated in a single Testrun.objects.bulk_update call at the end of process_flakes_for_commit.
4. Batch Expired Flake Updates: Individual flake.save() calls for expired flakes are replaced with appending to a list, which is then processed by a single Flake.objects.bulk_update call.

Impact:
This significantly reduces the number of database queries from N+1 (where N is the number of uploads) to a constant number of queries, improving the performance and efficiency of the ProcessFlakesTask.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. In 2022 this entity acquired Codecov and as result Sentry is going to need some rights from me in order to utilize my contributions in this PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

Fixes WORKER-YTD

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (7b60783) to head (e1a2b37).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1209      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50862    50877      +15     
  Branches     1626     1626              
==========================================
+ Hits        46741    46754      +13     
- Misses       3815     3817       +2     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.51% <9.09%> (-0.05%)	⬇️
workerunit	90.37% <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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