v0.2.0 of pqcrypto

Pure Dart post-quantum cryptography library. Starts with FIPS 203-aligned ML-KEM (Kyber) and future ML-DSA support. Flutter and Web compatible. Changelog excerpt: ### Added - Input validationfor encapsulate()and decapsulate()per FIPS 203 §7.2/§7.3: - Public key length and modulus checks (non-canonical coefficient rejection via ByteEncode₁₂ ∘ ByteDecode₁₂round-trip). - Secret key length and embedded H(pk)integrity check. - Ciphertext length check. - Pack.decodeSecretKeylength guard. - OpenSSL interoperability tool(tool/openssl_interop/): dart:ffi-based harness proving wire-level ML-KEM-768 compatibility with OpenSSL ≥ 3.5. [...]