Fix symbol-table and typeglob slot semantics exposed by Symbol::Util

[fglock]

Summary

Symbol::Util 0.0203 exposes incorrect package-stash and typeglob-slot behavior in PerlOnJava. The distribution is pure Perl and its unchanged upstream suite passes under system Perl, so this is a PerlOnJava language-compatibility defect rather than an XS, service, or environment limitation.

Fixing the underlying semantics should benefit other modules that inspect or modify symbol tables.

Results

From CPAN random-tester run 20260825-132251-83655:

• PerlOnJava: 262/307 assertions pass; 45 fail across 4/8 test programs.
• System Perl in the same usable environment: 307/307 assertions pass across all 8 test programs.

Failing upstream test files:

• t/10use.t: a package expected to have no imported functions unexpectedly contains a DATA stash entry.
• t/40delete_glob.t: selective and complete glob deletion/restoration mishandles SCALAR, ARRAY, HASH, CODE, and IO slots.
• t/70export_glob.t: exporting individual slots can expose unwanted CODE slots, including when the selected source slot does not exist.
• t/80export_package.t: filtered exports and unexports leave unwanted CODE slots, and mixed-slot unexport operations do not remove the requested slots correctly.

The other four test files pass, including basic glob fetching, stash access, subroutine deletion, and glob-slot listing.

Expected behavior

PerlOnJava should preserve Perl's independent typeglob-slot semantics:

• assigning one slot must not make unrelated slots visible;
• deleting selected slots must retain only the intended slots;
• deleting a complete glob through its package stash must remove it;
• restoring backed-up slots must reproduce the original glob;
• package stashes must not acquire unrelated DATA or phantom CODE entries.

Ecosystem impact

A targeted MetaCPAN reverse-dependency lookup found four released distributions with direct runtime requirements on Symbol::Util:

• MySQL-Util
• namespace-functions
• Test-Assert
• constant-boolean

None were classified as recent dependants. The direct count is modest, but this issue concerns reusable core Perl semantics and may affect modules that manipulate typeglobs without declaring Symbol::Util.

Suggested acceptance criteria

• Add focused project-owned regression tests for independent glob-slot assignment, deletion/restoration through a package stash, and absence of phantom CODE/DATA entries.
• Validate those tests with system Perl first.
• Make the focused tests pass on both PerlOnJava backends.
• Make the unchanged Symbol::Util 0.0203 suite pass.