Compute Failure Summary new-failure flags in render without mutating props

[camd]

Summary

FailureSummaryTab.render() mutated its own props on every render — it set selectedJob.newFailure and toggled suggestion.showNewButton on the suggestion objects while building the output. This makes render impure and can produce subtle bugs when React reuses those objects across renders.

This change derives those values during render instead:

• Replace the mutation loop with an isNewFailureLine() predicate plus local newFailureCount and firstNewFailureIndex.
• Pass showNewButton to SuggestionsListItem as an explicit prop instead of mutating suggestion.showNewButton; the item now reads it from props.

Behavior is preserved: the banner still counts every qualifying "new failure" line, and only the first qualifying line is flagged with the NEW button.

Testing

• Added unit tests covering the new-failure banner count and the single-NEW-flag behavior.
• Full FailureSummaryTab suite passes (8 tests).
• Lint clean.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.59%. Comparing base (740daac) to head (dfdec8d).

Files with missing lines	Patch %	Lines
...shared/tabs/failureSummary/SuggestionsListItem.jsx	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9668   +/-   ##
=======================================
  Coverage   82.59%   82.59%           
=======================================
  Files         622      622           
  Lines       36580    36577    -3     
  Branches     3279     3276    -3     
=======================================
- Hits        30213    30212    -1     
+ Misses       6217     6215    -2     
  Partials      150      150           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.