Release v3.3.1

Picks up Chronicle's 19.0.1 kernel release, including the fix for a connect-time compatibility check that could reject a client which had only gained fields since the server's release (Cratis/Chronicle#4058).

mix.exs deliberately keeps a loose lower bound on this dependency (see the comment there), so the actual upgrade is mix.lock moving forward via mix deps.update cratis_chronicle_contracts. The hand-written @protocol_version constant in AppendCompatibility — kept separate from the package's own runtime version because that self-reports "0.1.0" — needed updating by hand alongside it; append_compatibility_test.exs exists specifically to catch the two drifting apart, and correctly failed until this constant was updated.

mix compile && mix test — 450 tests pass, 6 pre-existing skips, no new warnings.