The previous fix used `suppress_non_speech_tokens` which doesn't exist
in pywhispercpp's C++ bindings (whisper.cpp uses `suppress_nst` but it's
not exposed). This caused initialization error:
"_pywhispercpp.whisper_full_params object has no attribute suppress_non_speech_tokens"
Changes:
- Remove invalid `suppress_non_speech_tokens` parameter
- Add `no_speech_thold=0.6` and `entropy_thold=2.4` for better filtering
- Add `_filter_non_speech()` post-processing function that filters:
- [BLANK_AUDIO] and other bracketed tokens
- Music notes (♪♫♬♩♭♮♯)
- Pure punctuation sequences
- Low speech-content text (<30% alphanumeric)
Fixes#219
