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

[sentry]

This PR addresses an N+1 query issue identified in the ProcessFlakesTask, specifically within the process_flakes_for_commit function in apps/worker/services/test_analytics/ta_process_flakes.py.

Problem:
Previously, for each commit, the process_flakes_for_commit function would iterate through N uploads. For each upload, it would call process_single_upload, which in turn would perform a separate SELECT query via get_testruns(upload) and a separate Testrun.objects.bulk_update operation. This resulted in N SELECT queries and N UPDATE queries on the ta_timeseries_testrun table, leading to an N+1 performance bottleneck.

Solution:
To resolve this, the following changes were implemented:

1. Introduced get_all_testruns: A new function get_all_testruns(upload_ids) was added. This function now fetches all relevant Testrun objects for all given upload_ids in a single batched SELECT query, significantly reducing database round-trips.
2. Refactored process_single_upload: The signature of process_single_upload was updated to accept a pre-fetched list of Testrun objects directly, removing its internal get_testruns call and the bulk_update operation.
3. Optimized process_flakes_for_commit: This function now first collects all upload.ids. It then calls get_all_testruns once to retrieve all necessary Testrun objects. After processing these Testrun objects in memory via process_single_upload, a single Testrun.objects.bulk_update is performed at the end of the loop for all modified Testrun instances.

Impact:
This change reduces the database operations for fetching and updating Testrun objects from O(N) (where N is the number of uploads) to O(1), drastically improving the performance and reducing the load on the database during flake processing.

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Fixes WORKER-YNB