Early exit node/graph

[ImLucasBrown]

Is your feature request related to a problem? Please describe.
Ability to cleanly exit a node or entire build.

Describe the solution you'd like
Lucas:

Something like return in the code block to early exit the node's execution.
Something like exit() or halt() to gracefully stop the graph from executing.
Currently these can be handled with crazy indentation and raising an exception (respectively).

Michael:

I like something explicitly nxt oriented for stopping the full graph. like graph_stop(). What are the ramifications for sub graphs? Does this only halt local subgraph or full super graph? Additionally can there(should there?) be ways to skip hierarchy stop_siblings() or skip_descendants()?

[neilberard]

Just wanted to chime in that I also think this would be a powerful feature for testing. Maybe it could work in the same way you add a start point that executes the hierarchy, you place a stop point that blocks the rest of the hierarchy as well.