Fix bundled CPAN module regressions

[fglock]

Summary

• Fix weak-reference lifetime handling exposed by DBIx::Class by deferring auto weak sweeps while temporary roots protect return-value assignment handoff.
• Add bundled CPAN fixes for Class::DBI and XML::TreePP, including distroprefs/patches and missing bundled support modules used by their dependency chains.
• Add regression coverage for weak cache cleanup after failed construction, returned object handoff assignment, and slice context behavior.

Notes

The Class::DBI patch is not a test bypass. Class::DBI objects overload boolean context, so the live-object cache must test ref rather than truthiness. Class::DBI already uses the same ref pattern in its HasA relationship code because overloaded objects may appear false.

DBIx::Class uncovered a separate runtime lifetime issue: an immediate weak sweep could run while a returned object graph was only protected by temporary roots during caller assignment. The runtime fix is generic and does not special-case DBI or DBIx::Class.

Verification

• make
• make test-bundled-modules
• timeout 3600 ./jcpan -t DBIx::Class
• timeout 1800 ./jcpan -t Class::DBI
• timeout 900 ./jcpan -t XML::TreePP
• New unit tests validated with system perl before jperl
• git diff --check