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

[sentry]

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

Problem:
Previously, process_flakes_for_commit iterated through each upload and called get_testruns() for every single upload, leading to an N+1 query pattern. Additionally, handle_pass performed individual flake.save() operations when a flake reached its expiration criteria, causing further redundant database writes.

Solution:

1. Batched Testrun Fetching: The get_testruns() function was replaced with get_testruns_for_uploads(). This new function fetches all relevant Testrun objects for all uploads in a single batched query, significantly reducing database round-trips.
2. Optimized process_single_upload: The process_single_upload function was refactored to accept a list of pre-fetched Testrun objects, eliminating the need for individual database queries within the loop.
3. Consolidated Bulk Updates: Testrun.objects.bulk_update is now called once after all uploads have been processed, rather than once per upload.
4. Deferred Flake Saving: Individual flake.save() calls in handle_pass were removed. Expiring flakes are now marked for update and handled by the existing Flake.objects.bulk_create (with update_conflicts=True) at the end of process_flakes_for_commit, ensuring all flake updates are batched.

These changes drastically reduce the number of database queries, improving the performance and efficiency of the ProcessFlakesTask.

Legal Boilerplate

Look, I get it. The entity doing business as "Codecov" is owned by Harness, Inc. In 2026 Harness acquired Codecov and as a result Harness 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 Harness can use, modify, copy, and redistribute my contributions, under Harness's choice of terms.

Fixes WORKER-YYR