Fix cross-ring copies and procedure lifetime cleanup

[cxzhong]

Summary

• Reorder matrix polynomial copies when source and destination rings do not share the same polynomial representation, while preserving the compatible fast path.
• Make procedure destruction safe and transactional while procedures are executing, including nested packages/rings, lists, htables, attributes, assignment, export, reload, examples, and branch calls.
• Restore normal PROC_CMD attribute cleanup and protect procedure metadata for the full call lifetime.
• Add focused regressions for procedure ownership/lifetime and cross-term-order mp_Copy, plus compiler-warning cleanups in touched code.

Testing

• Release and OM_TRACK builds completed successfully.
• Modified Singular translation units passed -Wall -Wextra -Werror; the standalone library parser passed the same gate.
• Modified libpolys units passed with warnings-as-errors after excluding two pre-existing header-only categories (unused-parameter and unused-value).
• make -j2 check passed.
• libpolys tests: 4/4 passed.
• proc_lifetime.tst: release 1/1 and OM_TRACK 1/1 passed; generated baseline decoded and passed gzip -t.
• New.lst: 88/94 passed. The remaining six are environment-dependent failures caused by unavailable optional NTL/FLINT, gfanlib, or external rref support: bug_absprimdec, enumpoints, gfanlib, oscar3905, rref, and testParametrization_2.

Review

Three independent review passes covered mp_Copy, procedure lifetime/reference handling, and the complete release diff. No remaining P1/P2 findings were identified. Repeated list/attribute lifetime tests showed no memory growth.