Regression tests for Acumen's parallel interpreter

Last week Jan continued the work on Acumen's parallel interpreter. In preparation for the planned optimizations and alternative scheduling strategy experiments he adapted the property-based regression tests previously developed with Adam for the enclosure interpreter. Currently, changes to an Acumen model's object graph are not performed immediately during evaluation of a discrete step, as is the case with discrete scalar variable updates, but instead logged and performed once the discrete steps have stabilized. Jan wonders if it is possible to do away with these logs entirely without changing the semantics of object graph-manipulating models. The regression tests will be handy when attempting this optimization as they test functional equivalence of an interpreter against a pre-recorded baseline.