consensus: Sync: timeout event is only handled when receiving Block message

[fed-franz]

Summary

In the current implementation, the timeout event is not handled when the timeout expires but only when receiving the next Block message.

Relevant Context

When the node is synchronizing with a peer (OutOfSync mode), a timeout is set within which the next tip+1 should be received.
This timeout is meant to prevent synchronization from stopping the consensus loop indefinitely.

Detailed Description

Currently, the timeout is handled by OutOfSync's function on_event (Block message) in fsm.rs: if a block is received and the timeout has expired, the function returns true, making the node switch back to InSync mode. Similarly, this function is only invoked by the on_event (Block message) function of SimpleFSM.

Possible Solution

The expiration of the timeout should be a separate event handled upon expiration.