pub fn bch_create_checksum_regular(hrp: &str, data: &[u8]) -> [u8; 13]Expand description
Compute the 13-character BCH checksum for the regular code over the HRP-expanded preamble plus the data part.
data is the sequence of 5-bit values for the data part (header + payload),
not including the checksum. Returns the 13-element checksum array, ready
to append to data to form the full data-part-plus-checksum.
The algorithm runs polymod over hrp_expand(hrp) || data || [0; 13],
then XORs the result with MK_REGULAR_CONST to extract the checksum.