Join state_heaps and state_sockets

[jihgfee]

Currently state_heaps and state_sockets are required to have the same domain, as they both signify the existence of a node on the given ip.

To achieve this constructively, rather than propositionally, it is proposed to join the two maps: state_nodes : gmap ip (heap * sockets).

To recover current semantics it is possible to project the map into the original subcomponents, e.g. for the SocketStep relation. For this, one can use (state_nodes σ) .*2 (for the socket map).

This change requires lifting the state interpretation to remove the information that currently tie the two together. The change should not be visible to users, and thus examples do not need to be lifted manually.