Refactor JUnitReporter

[cpisciotta]

Changes

• Pass parsed CaptureGroup instead of raw xcodebuild output. This avoids duplicate parsing and better leverages type safety.
• Consolidate JUnitComponent parsing, avoiding the need for duplicate instantiation and optionals.
• Fix typos.

Testing

Validated that sample XCTest input parsed as a JUnit report using the debug executable.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.71%. Comparing base (de4629e) to head (6cfbb6d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #367      +/-   ##
==========================================
- Coverage   90.16%   89.71%   -0.45%     
==========================================
  Files          17       17              
  Lines        2470     2460      -10     
==========================================
- Hits         2227     2207      -20     
- Misses        243      253      +10     

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