perf(worker): Optimize flag comparison report generation

[sentry]

Fixes WORKER-Y7V. The issue was that: Flag.totals property repeatedly re-filters reports and re-calculates totals for each flag, causing N+1 computational overhead.

• Pre-fetch the comparison diff once per comparison instead of once per flag.
• Pre-fetch base report flags once per comparison.
• Cache filtered flag reports to avoid redundant calls to ReadOnlyReport.filter() when calculating totals and applying diffs.
• Refactor get_flag_comparison_totals to accept pre-fetched flag objects and the diff directly.

This fix was generated by Seer in Sentry, triggered automatically. 👁️ Run ID: 13353963

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Note

Medium Risk
Touches the worker’s flag comparison totals calculation, so mistakes could silently skew stored head/base/patch totals. Changes are localized and primarily performance-oriented but alter how filtered reports and diffs are reused per flag.

Overview
Speeds up flag comparison persistence by moving base-flag and comparison_proxy.get_diff() lookups out of the per-flag loop and refactoring get_flag_comparison_totals to accept the pre-fetched Flag objects plus the diff.

Within get_flag_comparison_totals, it now caches each flag’s filtered report (flag.report) for reuse when computing totals and applying diffs, and applies the diff via the cached filtered report (using apply_diff(diff, _save=False)) to avoid repeated filtering/allocation.

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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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[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.25%. Comparing base (9eed0bb) to head (28ea258).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #826   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files        1306     1306           
  Lines       48012    48015    +3     
  Branches     1636     1636           
=======================================
+ Hits        44294    44297    +3     
  Misses       3407     3407           
  Partials      311      311           

Flag	Coverage Δ
workerintegration	58.53% <0.00%> (-0.02%)	⬇️
workerunit	90.39% <100.00%> (+<0.01%)	⬆️

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