feat(ext/node): implement X509Certificate methods for Apple verifier

[fffzlfk]

Summary

Implement X509Certificate.raw, toString(), infoAccess, and verify() in the Node crypto polyfill. These methods are used by @apple/app-store-server-library@3.1.0 when initializing its signed data verifier; the current stubs raise ERR_NOT_IMPLEMENTED.

The Rust ops expose the certificate DER and PEM encodings, format Authority Information Access entries, and verify the certificate signature against a supplied KeyObject. Signature verification covers RSA PKCS#1 v1.5 with SHA-1/256/384/512 and ECDSA with SHA-256/384/512. A certificate fixture checks the encodings, OCSP URI, successful verification, and a tampered signature.

Related upstream Deno work: denoland/deno#32270

Validation

• cargo check -p ext_node and the targeted Rust unit test passed with this patch on the local Edge Runtime branch.
• RUSTUP_TOOLCHAIN=stable cargo fmt --all --check and git diff --check passed on this branch.
• Node.js confirmed the fixture's infoAccess, raw, toString(), and verify() output.
• The targeted Rust test could not be rerun against upstream main locally: its pinned Rust 1.98 toolchain is not installed, and the offline dependency cache lacks async-scoped.