[codex] expose X509 extension metadata

[andrewtdiz]

Summary

Refs #2563.

Adds a focused X509Certificate extension-metadata slice:

• exposes X509Certificate#subjectAltName for deterministic DNS/IP/email/URI SAN entries
• exposes X509Certificate#keyUsage as Node 26-shaped Extended Key Usage OID arrays
• keeps absent extension properties returning undefined
• adds an embedded extension-bearing certificate parity fixture

Scope

The implementation decodes the existing parsed X509 handle's extensions with RustCrypto x509-cert types and routes the two new properties through the handle property dispatcher.

This intentionally follows the Node 26 observed keyUsage shape for Extended Key Usage OIDs, not a broader Basic Key Usage flag surface.

Non-goals

Still intentionally outside this slice: checkHost() / checkEmail() / checkIP(), certificate/key verification, publicKey, issuerCertificate, infoAccess, and toLegacyObject().

Verification

• npm exec --package=node@26 -- node test-parity/node-suite/crypto/x509/extension-metadata.ts
• CARGO_TARGET_DIR=/tmp/perry-node-x509-check-target cargo check -p perry-stdlib --no-default-features --features crypto
• CARGO_TARGET_DIR=/tmp/perry-node-x509-check-target npm exec --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module crypto --filter extension-metadata'
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/tmp/perry-node-x509-check-target npm exec --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module crypto --filter x509'
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh