Fix silence detection

[aigerimmmm]

PR for the issue https://github.com/argmaxinc/WhisperKit/issues/27.

• Added SilenceDetectionFilter similar to LanguageDetectionFilter.
• Implemented detectSilence similar to detectLanguage in TextDecoder that does a single forward pass from to detect silence periods.
• Added tests for SilenceDetectionFilter.
• Added silence detection and segment skipping logic in TranscribeTask.
• Updated models to support silence detection:
  • Added flags in DecodingOptions for ignoring prefill prompts during silence detection.
  • Changed property for managing silence detection threshold.