crypt4gh-rust

Narrowed down the missing bit(s) to pass the test_keys in decipher()'s match ciphername block. /cc @mmalenic. This is the last bit that needs translated to RustCrypto's primitives, I'm fairly comfident that after writing the 'aes256-ctr' case correctly, we have 100% tests passing: https://github.com/umccr/crypt4gh-rust/blob/8b51711178963949c62daa7c07892a6141436d47/src/keys.rs#L369C2-L371

Clarify errors for failing tests, replace asserts for Crypt4GH errors