perry-stdlib: split crypto.rs and webcrypto.rs into per-algorithm submodules

[TheHypnoo]

Background

crates/perry-stdlib/src/crypto.rs (4997 lines) and crates/perry-stdlib/src/webcrypto.rs (2809 lines) grew past the 2000-line limit while #1419 expanded the node:crypto parity surface. Both are currently allowlisted in scripts/check_file_size.sh so CI passes.

crates/perry-hir/src/ir/expr.rs (2009 lines) also crossed the boundary; this is the Expr enum + the walker trait implementations, and the PR added the WebCrypto variants.

Goal

Move these out of the allowlist by following the chore/split-large-files pattern (v0.5.1019/v0.5.1020 commits).

perry-stdlib/src/crypto.rs

Split into per-algorithm-family submodules:

• crypto/hash.rs — Hash / Hmac (already partly factored as HashState / HmacState).
• crypto/cipher.rs — CipherHandle, AES-CBC / GCM / KW.
• crypto/sign.rs — SignHandle, RSA-PKCS#1 v1.5 / RSA-PSS.
• crypto/ecdh.rs — EcdhHandle, ECDH P-256, X25519.
• crypto/dh.rs — DiffieHellmanHandle.
• crypto/kdf.rs — PBKDF2, scrypt, HKDF.
• crypto/random.rs — randomBytes, randomInt, randomUUID, randomFill.
• crypto/keys.rs — createSecretKey, generateKeySync, generateKeyPairSync, KeyObject helpers.
• crypto/prime.rs — generatePrime, checkPrime.
• crypto/util.rs — bytes_from_ptr, alloc_buffer_from_slice, encoding helpers.

perry-stdlib/src/webcrypto.rs

Same shape but for subtle.*:

• webcrypto/digest.rs, webcrypto/hmac.rs, webcrypto/aes.rs, webcrypto/ec.rs, webcrypto/rsa.rs, webcrypto/kdf.rs, webcrypto/wrap.rs, webcrypto/jwk.rs, webcrypto/util.rs.

perry-hir/src/ir/expr.rs

Variants are alphabetized today. Could split by surface family: expr/cryptographic.rs, expr/string.rs, etc. Higher risk because the walker traits need symmetric updates; consider doing this last.

Validation

After each split:

• cargo build --release --workspace clean.
• cargo test --release --workspace --exclude perry-ui-* passes.
• ./run_parity_tests.sh 100% on the touched module.
• Remove the corresponding line from scripts/check_file_size.sh ALLOWLIST.

Tracked under #793. Pattern reference: commits on chore/split-large-files for compile.rs and entries.rs.