[codex] fix Node Web Storage globals

[andrewtdiz]

Summary

Fixes #812.

• Return the rooted localStorage and sessionStorage objects from the reflected global descriptor getters instead of undefined.
• Give Storage.prototype.length its own receiver-aware getter so it keeps the existing illegal-invocation behavior.
• Allow internal storage mutations to refresh the readonly length data slot by clearing and restoring attrs around the update.
• Extend globals/storage-globals with descriptor getter coverage.

Root Cause

The Web Storage globals installed reflectable accessor descriptors, but the shared getter stub always returned undefined. After exposing the actual storage objects through the descriptor getters, storage mutations also hit an existing internal update path that wrote to the readonly length property through normal property assignment and threw.

Known Limit

This keeps the existing in-memory/process-local Web Storage behavior. It does not change persistence or flag handling.

Validation

• npm exec --package=node@26 -- node --experimental-webstorage --localstorage-file=/tmp/perry_web_storage_parity.sqlite test-parity/node-suite/globals/storage-globals.ts
• Manual Perry compile/run for globals/storage-globals, then diff -u /tmp/perry_storage_node.out /tmp/perry_storage_run.out clean
• CARGO_TARGET_DIR=/root/perry-worktrees/.build-targets/node-web-storage-globals npm exec --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module globals --filter storage-globals' -> pass, report test-parity/reports/parity_report_20260604_040722.json
• CARGO_TARGET_DIR=/root/perry-worktrees/.build-targets/node-web-storage-globals cargo check -p perry-runtime
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh