perf: Bulk-fetch testruns and update flakes in ProcessFlakesTask

[sentry]

This PR addresses an N+1 query performance issue identified in the app.tasks.flakes.ProcessFlakesTask, specifically within the services.test_analytics.ta_process_flakes.py module.

Problem:
Previously, process_flakes_for_commit would iterate over each upload and call process_single_upload, which in turn would execute a separate database query via get_testruns(upload) to fetch testruns for that specific upload. This resulted in an N+1 query pattern (1 query for uploads + N queries for testruns).
Additionally, handle_pass would perform individual flake.save() calls for each expiring flake, leading to further per-row database operations.

Solution:

1. Bulk-fetch Testruns: A new function get_testruns_for_uploads was introduced to fetch all relevant testruns for all uploads in a single database query using upload_id__in=[...]. These testruns are then grouped by upload_id in memory.
2. Optimized process_single_upload: The process_single_upload function was updated to accept the pre-fetched list of testruns, eliminating the need for individual database queries within the loop.
3. Bulk-update Expired Flakes: The handle_pass function no longer calls flake.save() directly. Instead, expired flakes are collected into a list (expired_flakes) and then bulk-updated in a single operation after the main processing loop in process_flakes_for_commit.

These changes significantly reduce the number of database queries executed during the ProcessFlakesTask, improving its performance.

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Fixes WORKER-YYM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (701e991) to head (fa829dd).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1413      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files        1325     1325              
  Lines       50868    50879      +11     
  Branches     1626     1626              
==========================================
+ Hits        46744    46753       +9     
- Misses       3818     3820       +2     
  Partials      306      306              

Flag	Coverage Δ
workerintegration	58.53% <11.11%> (-0.04%)	⬇️
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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