Add small accessors to the safe wrapper (tracking)

[uqio]

Tracking issue for the "Could add on demand" section of whispercpp/TODO.md. Each item is a 5–15 line wrapper around an existing FFI symbol; none is required for current callers but each is justifiable when a concrete need appears.

When picking one off:

• Confirm the FFI symbol is in whispercpp-sys/src/generated.rs. If not, extend the allowlists in whispercpp-sys/build.rs::generate_bindings_with_args().
• Replicate the safety pattern of the closest existing wrapper (non-null pointer, lifetime tied to parent struct, no aliasing across threads). Document the SAFETY block.
• cargo test -p whispercpp --features serde --lib should still pass.
• Add a doc test or unit test for the new accessor.

Token / vocab

• Context::token_to_bytes(token) -> Option<&[u8]> — non-UTF-8 byte sequences from BPE merges
• Context::tokenize_one(text) -> Option<i32> — wraps whisper_token_id
• Context::tokenize(text) -> Vec<i32> — wraps whisper_tokenize, useful as input to Params::set_tokens

Language helpers

• Context::lang_id_for(name: &str) -> Option<i32> — reverse of detected_lang, wraps whisper_lang_id
• pub const LANG_MAX_ID: i32 = … — wraps whisper_lang_max_id
• Lang::full_name() -> &'static str — wraps whisper_lang_str_full ("english" vs "en")

Special-token accessors

• Context::token_translate() -> i32, token_transcribe, token_prev, token_nosp, token_not, token_solm — force-prefix decoding seeds
• Context::token_for_lang(Lang) -> i32 — wraps whisper_token_lang

Model + state introspection

• Context::model_dims() -> ModelDims — small struct exposing whisper_model_n_audio_state, n_audio_head, n_audio_layer, n_text_state, n_text_head, n_text_layer, n_mels, model_ftype
• pub fn version() -> &'static str — wraps whisper_get_whisper_version
• State::n_mel_frames() -> i32 — wraps whisper_n_len_from_state

Timing helpers

• Context::print_timings() — wraps whisper_print_timings
• Context::reset_timings() — wraps whisper_reset_timings

Verify-against-existing

• Token::posterior() -> f32 is currently Token::p() reading whisper_token_data.p. Verify it agrees with whisper_full_get_token_p_from_state under temperature / wildcard sampling.

See whispercpp/TODO.md for the full table.