Add word-level timestamps and confidence scores

- New word_timestamps option (default False) in client handshake
- When enabled, each segment includes 'words' array with per-word
  start/end times and probability scores
- Wired through entire pipeline: client → server → backend → transcribe()
- Words include timestamp_offset for accurate absolute times
- REST API already supported word timestamps; now WebSocket does too
- Added 9 unit tests for word timestamp extraction and formatting

whisper_live/server.py

@@ -293,6 +293,7 @@ class TranscriptionServer:
                     translation_queue=translation_queue,
                     hotwords=options.get("hotwords"),
                     diarization=self._create_diarizer(options),
+                    word_timestamps=options.get("word_timestamps", False),
                 )
 
                 logging.info("Running faster_whisper backend.")