3b3eb2f78e
Implements Base26 encoding/decoding using uppercase A-Z as digits (A=0, B=1, ..., Z=25). Input bytes are interpreted as a big-endian unsigned integer and converted to/from radix 26. Includes tests for the reference vector (EAT -> JYGBS), round-trips, empty input, zero bytes, and binary data. Closes gchq/CyberChef#1511