Function decode_prefixed 

pub fn decode_prefixed(expected: Tag, s: &str) -> Result<Zeroizing<Vec<u8>>>

Decode a tag_<hexbody>_<hexchecksum> string, verifying both the tag and the checksum, and return the raw payload bytes.

The returned bytes are wrapped in Zeroizing so that decoding a secret key does not leave a readable copy on the heap once the caller is done with it.

Errors:

• Error::InvalidPrefix if the string is not in three-part shape, or its tag is not the one expected for this type;
• Error::InvalidHex if the body or checksum part is not hex;
• Error::InvalidChecksum if the checksum is the wrong length or does not match the recomputed value.