Exclude test and benchmark files from patch coverage

[glen-84]

Summary

• Patch coverage now excludes test and benchmark sources (any path with a /test/, /tests/, /benchmark/, or /benchmarks/ segment), so both the patch percentage and the project coverage total reflect production code only.
• Test projects instrument their own code, so changed test files were being counted (often at 0%), skewing the patch percentage, and test assemblies inflated the project-total denominator. Both are now dropped from the table, the JSON, the headline patch %, and the project coverage line, via a single IsProductionPath helper.

Test plan

• Verified a changed, instrumented test file is excluded from the report output.
• Confirmed on a real PR: production paths remain; the patch headline is unaffected where test files were already non-instrumented; the project total rises once test assemblies leave the denominator (49.3% → 52.3%).

[Copilot]

Pull request overview

Updates the patch coverage GitHub script to exclude test and benchmark sources from patch coverage calculations so the reported percentage reflects production code changes only.

Changes:

• Skip changed paths that contain /test/, /tests/, /benchmark/, or /benchmarks/ segments when building patch coverage rows.
• Ensure excluded paths are omitted from the markdown table, JSON payload, and headline totals by filtering them out at row-construction time.

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