fix: ignore malformed default input messages

[VivekJJadav]

Summary

Fixes a reliability issue in DefaultInputHandler where a malformed websocket input message could stop the input listener entirely.

Previously, process_message() accessed message["type"] and message["data"] directly. If a client sent a malformed payload, the resulting exception was caught by _listen() as a fatal error, causing the handler to send EOS to the transcriber and stop processing future messages.

Changes

• Validate that incoming messages are dictionaries before routing them
• Guard audio and text messages that are missing data
• Keep the listener alive after malformed input
• Add an async regression test covering malformed input followed by valid text input

Test

.venv/bin/python -m pytest -q tests/tests/test_default_input_handler.py