Function decode_string 

pub fn decode_string(s: &str) -> Result<DecodedString, Error>

Decode an mk1 string, validating HRP, case, length, and checksum.

Performs full BCH error correction up to four substitutions (t = 4 capacity of the BCH(93, 80, 8) regular code and the BCH(108, 93, 8) long code), via syndrome-based Berlekamp–Massey + Forney decoding (implemented in the sibling bch_decode module).

Errors:

• Error::MixedCase if the string mixes upper and lower case.
• Error::InvalidHrp if the HRP is missing or not crate::consts::HRP.
• Error::InvalidStringLength if the data-part length isn’t a valid mk1 length.
• Error::InvalidChar if the data part contains a non-bech32 character.
• Error::BchUncorrectable if the checksum can’t be repaired within the BCH t = 4 correction radius.