Updates to support loop break

[ColinCarterUK]

in unconstrained loops. Constrained loops and breaks to follow.

This updates the constraint checking logic in Job.AssessingConstraints state. It now checks that for all XOR constrained events there are the same number of graph edges after the event as there are events (since for every event there can be only a single exit branch taken).

[github-actions[bot]]

Test results for branch "MUN-143_Loop_break_topology": https://s3.amazonaws.com/1f-outgoing/munin/MUN-143_Loop_break_topology/index.html Permanent link for this run: https://s3.amazonaws.com/1f-outgoing/munin/82e94b4/index.html