v0.2.2

Bump version to 0.2.2, fix encode_batch panic, DRY refactors, doc fixes

- Fix .unwrap() in encode_batch that could crash the BEAM on allocation failure
- Extract decoder_decode_chunk_impl to DRY up Rust NIF code
- Extract route_nif/4 and normalize_result/1 to DRY up Elixir layer
- Remove unsupported HZ encoding from docs
- Clarify encoding count (40 encodings, 200+ aliases)
- Fix stream/2 docs incorrectly claiming 1:1 output correspondence
- Add stream flush tests for incomplete trailing sequences
- Bump Cargo.toml version to match mix.exs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>