crypto: WebCrypto error paths should reject with DOMException instead of resolving undefined

[TheHypnoo]

Background

The node:crypto.subtle.* surface (perry-stdlib/src/webcrypto.rs) currently resolves to undefined on invalid inputs, missing keys, or unsupported algorithms. Node returns a rejected Promise with a DOMException("OperationError" | "NotSupportedError" | ...) in those cases.

Impact

• Code using .catch(e => e.name === "OperationError") diverges from Node — Perry runs the then branch with undefined.
• Parity tests that exercise error paths cannot be written against the current surface.
• Surfaced during the Expand crypto parity coverage #1419 review; deferred as out-of-scope (157 sites, no rejection-path test coverage to validate behavior changes).

Scope

• Add a reject_with_dom_exception(name: &str, message: &str) -> *mut Promise helper in webcrypto.rs.
• Audit each resolve_undefined() site in webcrypto.rs (~157) and convert those that signal an error to use the new helper. Legitimate "resolve undefined" cases (e.g. void returns) stay as-is.
• Add a parity suite for rejection behavior: test-parity/node-suite/crypto/webcrypto/errors/*.

Tracked under #793.

[proggeramlug]

Partial slice landed in #1553 (commit fb7e6b9): adds reject_with_dom_exception helper + converts the top-level error paths in digest, importKey, exportKey, sign, verify, encrypt, decrypt, generateKey, deriveKey, wrapKey, unwrapKey (the cases where the algorithm name itself is unrecognized, the key isn't a registered CryptoKey, the format string is unsupported, or the key bytes are empty). Parity tests under test-parity/node-suite/crypto/webcrypto/errors/ pin down the no-silent-resolve invariant for digest, importKey, and sign.

Remaining: inner failures (algorithm/key-kind mismatches, RSA DER parse errors, decrypt MAC failures) — those need per-site classification (OperationError vs DataError vs InvalidAccessError). Roughly ~140 of the original 157 resolve_undefined() sites still need this audit. Leaving issue open.