refactor: replace asyncio.gather with asyncio.wait for better task lifecycle management

[battlecook]

Checklist

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PR Description

refactor: replace asyncio.gather with asyncio.wait for better task lifecycle management

• Replace asyncio.gather() with asyncio.wait(return_when=FIRST_COMPLETED) in both server and client

Files changed:

• moshi/server.py: Update handle_chat method's task management
• moshi/client.py: Update Connection.run method's task management

CLA
I, battlecook, confirm that I have read and understood the terms of the CLA of Kyutai-labs, as outlined in the repository's CONTRIBUTING.md, and I agree to be bound by these terms.