Describe the bug

In Transports::set_used ezk_sip_core expects a TpHandle to always be returned from a MangedTransport, however this is not always the case. In this line of MangedTransport::try_get:

            let owner = weak_tx.upgrade()?;

an upgrade from a weak pointer to an Arc is attempted, which may fail if the object is already deallocated. The method in here is called when a message is received in a separate task for receiving messages.

How to reproduce

This fails when dropping the transaction before the last message arrives.
This will drop the Arc, which the weak is trying to upgrade to upon receiving the reply to the message however the receiver may still receive KeepAlive messages, causing this bug to occur.

I'm aware that this version of ezk-sip-core is outdated but just wanted to post this issue here in case anyone else runs into it.
The solution would be to make the set_used method fallible and a workaround is to drop the transaction at a later time.