Minimal ASN.1/DER/PEM/Base64 codec implemented in C with no OpenSSL dependency. Designed for post-quantum key serialization (SPKI, PKCS#8) but usable for any scheme that needs DER TLV encoding, Base64 with PEM line wrapping, and PEM armor parsing. Used by the ml_dsa gem and reusable by ML-KEM, SLH-DSA, and other PQC implementations.