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

[sentry]

This PR addresses an N+1 query performance issue within the app.tasks.flakes.ProcessFlakesTask.

Problem:
Previously, the process_flakes_for_commit function would iterate through each ReportSession (upload) and, for every upload, call process_single_upload. Inside process_single_upload, get_testruns(upload) was invoked, leading to a separate database query for Testrun objects for each individual upload. This resulted in an N+1 query pattern, where N is the number of uploads.

Additionally, within handle_pass, when a flake reached 30 passes and was considered expired, flake.save() was called individually for each such flake, leading to multiple single-row updates.

Solution:

1. Batched Testrun Fetch: A new function, get_testruns_for_uploads, was introduced. This function now fetches all relevant Testrun objects for all uploads associated with a commit in a single batched database query. The results are then grouped in memory by upload_id.
2. Refactored Processing Flow: process_flakes_for_commit now calls get_testruns_for_uploads once before iterating through uploads. process_single_upload was updated to accept the pre-fetched and grouped testruns, eliminating the per-upload database calls.
3. Bulk Expired Flake Update: The handle_pass function no longer calls flake.save() directly. Instead, expired Flake objects are collected into a list (expired_flakes). After the main processing loop in process_flakes_for_commit completes, these collected expired flakes are updated in a single bulk_update operation.

Impact:
These changes significantly reduce the number of database queries, transforming multiple individual queries into single, efficient batched operations. This improves the performance and reduces the load on the database when processing flakes.

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Fixes WORKER-YZ1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (701e991) to head (dab2b40).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1431   +/-   ##
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  Coverage   91.89%   91.89%           
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  Files        1325     1325           
  Lines       50868    50874    +6     
  Branches     1626     1626           
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+ Hits        46744    46750    +6     
  Misses       3818     3818           
  Partials      306      306           

Flag	Coverage Δ
workerintegration	58.54% <12.50%> (-0.03%)	⬇️
workerunit	90.37% <100.00%> (+<0.01%)	⬆️

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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