Teach simulator about the different "layers" of execution

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It Would Be Nice (TM) if the API to the QVM allowed access to the various "layers" of tensor factors in the execution. The QVM ought to understand (for noise/programmatic/etc) that

H 0
H 1

are logically in the same "layer".

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Maybe start with a function

MAP-LAYERS (f instructions &key strategy)

where f : [Instructions] -> (), instructions : [instruction], and strategy is from at least {:trivial, :greedy}.

:trivial would just map one instruction at a time. :greedy would be "circuit-style" earliest first based off of resource.

This could be plugged into the middle of RUN and TRANSITION as a middle-man, maybe TRANSITION-COMMUTING-GROUP which gives implementers freedom in how transition is run while remaining true to QAM semantics.