Migrate to WhisperX for speaker diarization

Implement a sliding window audio buffer and update the transcriber to
use WhisperX for transcription, alignment, and speaker identification.
Update the pipeline to handle and store speaker-attributed transcripts.

Additionally, update the LLM processor's reasoning parameter to
"enable_thinking".

requirements.txt

@@ -1,5 +1,5 @@
 # Core dependencies for D&D Helpers
-faster-whisper
+whisperx
 sounddevice
 pydantic
 textual