[codex] honor child_process uid gid options

[andrewtdiz]

Summary

• add child_process parity coverage for uid/gid across spawn, spawnSync, execFileSync, and fork when running as root
• apply numeric uid and gid options through the shared child_process command setup
• set gid before uid on Unix so dropped-privilege children observe the supplied identities

Root Cause

Perry parsed common child_process options such as cwd and env, but ignored uid and gid. Node applies these IDs before exec, so root-launched children should observe the supplied IDs via process.getuid() and process.getgid().

Validation

• npm exec --yes --package=node@26 -- node --experimental-strip-types test-parity/node-suite/child_process/async/uid-gid.ts
• Baseline check before the fix: focused parity reported Node.js: spawn uid gid: 65534:65534 and Perry: spawn uid gid: 0:0
• npm exec --yes --package=node@26 -- bash -lc "./run_parity_tests.sh --suite node-suite --module child_process --filter uid-gid"
• npm exec --yes --package=node@26 -- bash -lc "./run_parity_tests.sh --suite node-suite --module child_process"
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh

Covers the uid / gid option slice of #2555.