EC keygen now returns proper SPKI DER instead of raw point bytes.
RSA keygen uses caller-supplied exponent via new_with_exp() and
validates key size to 2048/3072/4096. Keybox parser extracts leaf
subject DN (not issuer). Added AttestKey=7 to KeyPurpose. Realigned
error variants with spec.
Splits concatenated DER cert chains into individual certificates,
extracts leaf issuer DN and notAfter via x509-cert crate. Handles
multi-byte DER length encoding (0x81-0x84).
Cargo.toml with 16 dependencies per build spec, error types with
From impls for all upstream error types, CertGenParams mapping the
full JNI config contract, EC/RSA key generation via ring and rsa crates.
Compiles clean for aarch64-linux-android via cargo-ndk.