[MM-59548] Fix potentially stuck goroutines

[streamer45]

Summary

Looking at goroutines profiles highlighted a couple of (unrelated) issues:

1. Some read calls on incoming voice tracks can suddenly block due to an apparent regression upstream (pion/transport).
   • This is still under investigation. Downgrading to the previous version is enough to prevent the issue while a fix is found.
2. The CloseSession could get stuck indefinitely in case of a timeout during the initial signaling phase due to a circular check on the session's done channel.
   • Reworked the function to preemptively close the channel in these fail-early cases.

Ticket Link

https://mattermost.atlassian.net/browse/MM-59548

[cpoile]

Huh, tricky. Nice fix. 🎉