[codex] expose subtle encapsulation method surface

[andrewtdiz]

Part of #2518.

Scope

• Exposes SubtleCrypto.prototype.encapsulateBits, decapsulateBits, encapsulateKey, and decapsulateKey with Node-shaped callable method names, lengths, and enumerable/writable/configurable descriptors.
• Routes direct crypto.subtle calls plus captured/dynamic crypto.subtle method calls through the WebCrypto dispatcher instead of surfacing undefined.
• Matches Node 26 missing-argument behavior by returning a rejected Promise with TypeError [ERR_MISSING_ARGS] and the WebIDL-style message.
• Returns an explicit unsupported WebCrypto rejection for non-missing encapsulation execution paths rather than silently missing the method.

Non-goals

• Implementing ML-KEM encapsulation/decapsulation execution.
• Advertising ML-KEM support through SubtleCrypto.supports().
• Changing P-384/P-521 WebCrypto support, which is tracked separately.

Validation

• npm exec --yes --package=node@26 -- node test-parity/node-suite/crypto/webcrypto/subtle-encapsulation-methods.ts
• CARGO_TARGET_DIR=/tmp/perry-webcrypto-encap-check cargo check -p perry-hir -p perry-codegen -p perry-runtime -p perry-stdlib
• Direct Perry compile/run of test-parity/node-suite/crypto/webcrypto/subtle-encapsulation-methods.ts with PERRY_NO_AUTO_OPTIMIZE=1
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/root/perry-worktrees/.build-targets/perry-webcrypto-encap-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module crypto --filter subtle-encapsulation-methods'
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/root/perry-worktrees/.build-targets/perry-webcrypto-encap-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module crypto --filter subtle-supports'
• PERRY_NO_AUTO_OPTIMIZE=1 CARGO_TARGET_DIR=/root/perry-worktrees/.build-targets/perry-webcrypto-encap-build npm exec --yes --package=node@26 -- bash -lc './run_parity_tests.sh --suite node-suite --module crypto --filter global-webcrypto-globals'
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh

[andrewtdiz]

Closing as a duplicate of #4291, which already covers the same #2518 WebCrypto encapsulation method surface. Keeping review focused there.