Add close function to Audio|Video Source

[typester]

No description provided.

[davidzhao]

lg!

[typester]

After reading Lukas's comment, I was also unsure during implementation whether the Python side should be made async, so I’m leaving this as an open question.

Should we await self._join_handle or self._join_fut ? If the answer is yes, I think it would be better to implement this as an async aclose and include the logic to wait for them. What do you think? @davidzhao @theomonnom

[theomonnom]

Yes please, let's create a aclose function instead, we don't need to await the join handle but it is great to keep it async to be future proof on the future changes we could do