fix: proceeding timeout too short

[giangndm]

The default client invite timeout is currently 30 seconds for both the initiating and proceeding states. However, this duration is too short for some SIP providers.

To address this, we need to extend the timeout specifically for the proceeding state to prevent incorrect detection. Consider increasing it to 2 minutes.

[kbalt]

As far as I can see, the timeout should only exist in the Calling state (confusingly called Init here), so calls to receive may only be be cancelled in the Init state. But since that could cause transactions to be stuck indefinitely, this seems good enough for me for now.

Thanks for noticing!