greedy_topological_sort in musical score

[mpharrigan]

Similar to #1636, the get_musical_score_data function for displaying traditional, "musical score"-style circuit diagrams uses a topological sort to order the bloq instances within a decomposition.

• This should be changed to use greedy_topological_sort to match our expected heuristic of delaying allocations and hurrying frees
• It's not a straightforward replacement, since we're using topological_generations and using the generation index as part of our musical score data. The networkx function we're using in greedy_topological_sort doesn't return the generations -- just a sort order
• We're theoretically using the generation index, but we're not using it in practice. It's part of the MusicalScoreData and could be used by a better drawing routine to group subbloqs that can be executed in parallel, but our simple drawing routine doesn't do that right now, so you can use greedy_topological_sort and put garbage data in the topo_gen field and not observe any ill effects. This is how I made the diagram in the linked issue.