Release v1.2.8

Use stdlib Cipher#gcm_tag; fix build on Crystal 1.22 (#12)

Crystal 1.22's OpenSSL bindings define EVP_CTRL_GCM_* themselves, so
re-declaring them in lib LibCrypto raised 'already initialized
constant' and the shard no longer compiled. Drop the local bindings
and the manual EVP_CIPHER_CTX_ctrl call in favour of Cipher#gcm_tag.

Raise the declared Crystal floor to 1.22.0, the version the suite
(320 examples) is verified against; the previous '>=0.31.1' was wrong.


Claude-Session: https://claude.ai/code/session_01HT5gvYGR83U2M4DyA6NA6f

Co-authored-by: Claude <noreply@anthropic.com>