Use Is_disjoint optimization in Shadow Mode

[maxweng-sentry]

Address this issue:
https://linear.app/getsentry/project/report-merging-improvements-89f3063419db/overview

Primary Fix: Use the is_disjoint Optimization in Shadow Mode

The Report.merge() method has a built-in optimization that wasn't being used:

• is_disjoint=True: Defers expensive line-by-line merging, just appends coverage records
• finish_merge(): Performs actual merging in one pass at the end

Changes:
In libs/shared/shared/utils/merge.py

• Added a deduplicate_sessions function that will run within finish_merge that will correctly merge LineSessions

In apps/worker/services/processing/merging.py

• Added Shadow Mode run of the function that will throw an exception if the optimized code is different from production code.

[sentry]

Codecov Report

❌ Patch coverage is 91.86047% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.83%. Comparing base (f3d65a6) to head (6962fa5).
⚠️ Report is 13 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/worker/services/processing/merging.py	91.78%	6 Missing ⚠️
libs/shared/shared/reports/resources.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #538      +/-   ##
==========================================
+ Coverage   93.82%   93.83%   +0.01%     
==========================================
  Files        1280     1282       +2     
  Lines       46120    46336     +216     
  Branches     1511     1527      +16     
==========================================
+ Hits        43272    43480     +208     
- Misses       2540     2547       +7     
- Partials      308      309       +1     

Flag	Coverage Δ
apiunit	96.53% <ø> (+0.01%)	⬆️
sharedintegration	38.71% <30.76%> (-0.21%)	⬇️
sharedunit	88.77% <92.30%> (+0.07%)	⬆️
workerintegration	58.89% <84.93%> (+0.13%)	⬆️
workerunit	91.02% <64.38%> (-0.12%)	⬇️

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[codecov-notifications]

Codecov Report

❌ Patch coverage is 91.86047% with 7 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/worker/services/processing/merging.py	91.78%	6 Missing ⚠️
libs/shared/shared/reports/resources.py	50.00%	1 Missing ⚠️

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[codspeed-hq]

CodSpeed Performance Report

Merging #538 will not alter performance

_{Comparing max/optimize-merge (6962fa5) with main (7bb8f94)¹}

Summary

✅ 9 untouched

Footnotes

1. No successful run was found on main (c55b19e) during the generation of this report, so 7bb8f94 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩