Add Telnyx media streaming Python example

[a692570]

Summary

• adds a Python Telnyx Media Streaming WebSocket example
• decodes L16, PCMU, and PCMA media payloads into float samples for Moonshine streaming transcription
• documents how to start a Telnyx stream with L16 and lists the example in the root README

Testing

• PYTHONPATH=python/src /tmp/moonshine-pr-venv311/bin/python examples/python/telnyx-media-streaming/telnyx_media_streaming.py --help
• /tmp/moonshine-pr-venv311/bin/python -m py_compile examples/python/telnyx-media-streaming/telnyx_media_streaming.py
• decoder checks for L16 conversion and Telnyx track filtering
• git diff --check
• secret scan over the diff found no matches

Notes

Telnyx Media Streaming sends WebSocket start and media events with media_format metadata and base64 audio payloads. Reference: https://developers.telnyx.com/docs/voice/programmable-voice/media-streaming