Complete Perl threads phases 31-34

[fglock]

Summary

• complete native callback/runtime ownership and detached-thread lifecycle work
• validate nested shared graphs atomically and preserve runtime identity across snapshots
• coordinate Unicode user properties without serializing unrelated runtime families
• fix non-local labeled control flow cleanup across eval and subroutine boundaries
• document the supported phases 31-34 tranche and keep runtime pooling deliberately disabled

Validation

• make — 962 tests, all passing (2 skipped)
• make check-links — 538 links checked, 0 errors
• new Perl units on system Perl — 5 files, 17 assertions, all passing
• dynamic map/reduce example — identical output on system Perl, JVM, interpreter, and virtual-thread mode
• focused DBIx regression t/35exception_inaction.t — 3/3 passing
• timeout 3600 ./jcpan --jobs 8 -t DBIx::Class — 325 files, 42,671 assertions, all passing

Notes

Runtime pooling remains disabled because closing a runtime is terminal and the documented fresh-runtime equivalence contract is not yet satisfied.