Speechmatics-python

Changed

- Renamed `extra_headers` to `additional_headers` in `websockets.connect()` to support WebSockets version 14.0,
as per [documentation](https://websockets.readthedocs.io/en/stable/howto/upgrade.html#arguments-of-connect)
- Updated `speechmatics-python` to require `Python >= 3.9`, aligning with WebSockets 14.0

speechmatics-python `2.0.3` is the last version supporting `Python 3.8`

Fixed

- Unexpected `keyword argument 'extra_headers'` error in `websockets.connect()`
by updating requirements to allow versions of websockets from 10.0 up to and including 13.1

Added

- Added internal, Speechmatics only client message: GetSpeakers, and server message: SpeakersResult
- Added internal, Speechmatics only client method: send_message

Changed

- Refactor mutable default parameters in run function

Changed

- Remove deprecated speaker_change, channel_and_speaker_change, and speaker_change_sensitivity diarization options
- Remove speaker change deprecation warning

Added

- Speaker change deprecation warning