fix(macos): parse numeric-prefixed sample thread rows

[tcconnally]

Summary

• Parse the numeric-prefixed Thread_... rows emitted by current macOS sample output.
• Preserve the existing unprefixed Thread ... fixture format.
• Add a regression fixture using the captured Call graph shape.

Reproduction

A real M5 capture contained native labels for libmpv, libavcodec, WindowServer, and Python, but the parser returned sample_threads_missing because rows such as 2930 Thread_1168979 ... did not match the old expression.

Verification

• Focused test was RED before the parser change: 7 passed, 1 failed.
• Focused test is GREEN after the change: 8 passed.
• python3 tests/run_all.py: PASS on the exact candidate.
• python3 -m compileall -q hyperwall scripts tests: PASS.
• git diff --check: PASS.

This parser fix does not claim native playback qualification or close the open native profiling work.