[codex] Respect symbol enumerability in Object.assign

[andrewtdiz]

Addresses #3986.

Summary

• Store descriptor attributes for symbol-keyed properties defined with Object.defineProperty.
• Include symbol-keyed data/accessor descriptors in Object.getOwnPropertyDescriptor.
• Make Object.assign skip non-enumerable symbol data properties while preserving direct-assignment defaults.
• Add GC scanning/reset coverage for the new symbol descriptor metadata table.

Why This Cut

#4161 handled the Object boxing portion of #3986. This PR covers the remaining coherent Object.assign descriptor/copy tail: the same symbol descriptor metadata is needed both for descriptor round-trips and for deciding whether a symbol property is enumerable during assignment.

Tests

• CARGO_TARGET_DIR=/root/perry-worktrees/perry-object-assign-tail/target cargo test -p perry-runtime symbol_define_property_attrs_round_trip_descriptor
• CARGO_TARGET_DIR=/root/perry-worktrees/perry-object-assign-tail/target cargo check -p perry-runtime -p perry-stdlib -p perry
• CARGO_TARGET_DIR=/root/perry-worktrees/perry-object-assign-tail/target npm exec --yes --package=node@26 -- bash -lc 'node --version; ./run_parity_tests.sh --suite node-suite --module object --filter assign'
  • Node v26.3.0
  • 3 pass / 0 fail / 0 compile fail
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh

Non-Goals

• Does not change unrelated Proxy/Reflect object-copy hooks.
• Does not broaden unrelated descriptor APIs beyond the symbol-keyed getOwnPropertyDescriptor behavior needed for this Object.assign cut.