fix(worker): N+1 query in test analytics flake processing

[sentry]

This PR addresses an N+1 query issue identified in the app.tasks.flakes.ProcessFlakesTask (WORKER-YP1), specifically within the services.test_analytics.ta_process_flakes module.

Problem:
Previously, process_flakes_for_commit would iterate over each upload and call process_single_upload, which in turn would execute get_testruns(upload). This resulted in a separate database query for testruns for each upload, leading to an N+1 query pattern. Additionally, handle_pass was performing individual flake.save() calls when a flake expired, causing further per-row database updates.

Solution:

1. Batch-fetch Testruns: Introduced get_testruns_for_uploads to fetch all relevant testruns for all uploads in a single database query. The results are then grouped by upload_id in Python.
2. Refactored process_single_upload: Modified process_single_upload to accept a list of pre-fetched testruns, eliminating its internal database query.
3. Deferred Flake Expiry Updates: Instead of immediate flake.save() calls in handle_pass, expiring flakes are now collected into a list (expiring_flakes) and updated in a single Flake.objects.bulk_update call after all uploads have been processed.
4. Materialized Uploads Queryset: The uploads queryset is now explicitly converted to a list to ensure it's evaluated once and consistently used.

These changes significantly reduce the number of database queries executed during flake processing, improving performance and reducing database load.

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Fixes WORKER-YP1