@W-23751646: Harden Python TCK coverage accounting

[mlischetti]

Summary

• align Python TCK discovery with exact corpus filename patterns and audit adjacent DWL module cases as structural skips
• validate structural policy and require every selected scenario to produce one accounted pytest result
• strengthen comparator and reporting regressions, including XML ordering, unknown charsets, xfail/XPASS accounting, and filtered runs
• ignore the generated Python .coverage database

Testing

• ./gradlew native-lib:pythonTest --rerun-tasks (86 passed)
• ./gradlew native-lib:stageTckSuites native-lib:pythonTck (711 passed, 37 skipped, 19 xfailed; 729 selected/accounted, 0 unaccounted)
• git diff --check