Go ValidateHashFormat was still validating the old -00 format
(algorithm:base64url with sha-256/sha-384/sha-512 prefix). Updated to
validate plain base64url without prefix per -01 spec and RFC 9449.
Python was already updated but uncommitted. Both refimpls now match.
Move Go reference implementation to refimpl/go-lang/ and add new
Python reference implementation in refimpl/python/. Update build.sh
with renamed draft and simplified tool paths.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
