Function decode 

pub fn decode(strings: &[&str]) -> Result<KeyCard>

Decode one or more mk1-prefixed strings into a KeyCard.

Supports both single-string and chunked inputs:

• One string with SingleString header → decode bytecode directly.
• One or more strings with Chunked headers → reassemble with cross-chunk-hash verification, then decode the bytecode.

Mixing SingleString and Chunked headers across a multi-string input is rejected with Error::MixedHeaderTypes. (An empty input list is rejected with Error::ChunkedHeaderMalformed — that’s the “no input at all” case, distinct from “header types disagree.”)