Organize SCC expansion module

[jcrozum]

@daemontus I forgot that I had never made a PR for this branch. We'll need to do some more work to make the expansion methods intuitive for the end-user still, but I think this is a necessary first step.

Moves some of the source scc logic to the SuccessionDiagram class (adds component_subdiagrams method) and to the interaction_graph_utils module (adds source_SCCs function). This finally gives a proper resolution to our cyclic import issues.

Also, functionality from the custom percolation function in expand_source_SCCs.py was integrated into space_utils.percolate_network as an option.

[github-actions[bot]]

Coverage Report

File	Stmts	Miss	Cover	Missing
balm
control.py	114	14	88%	107, 119, 125, 129, 134, 143–159, 477, 480, 493
interaction_graph_utils.py	38	4	89%	11–13, 151–152
motif_avoidant.py	148	2	99%	26, 181
petri_net_translation.py	149	11	93%	22–26, 79, 136, 305–306, 330–331, 340, 449
space_utils.py	132	4	97%	26–28, 414, 462
succession_diagram.py	280	17	94%	6, 188–193, 201, 261–262, 272, 278, 394, 584, 660, 851, 889, 926
symbolic_utils.py	26	3	88%	10–12, 102
trappist_core.py	183	30	84%	14–18, 55, 57, 92, 168, 215, 217, 219, 247–250, 254–256, 276–282, 340, 342, 372, 420, 422, 453, 506
balm/_sd_algorithms
compute_attractor_seeds.py	30	1	97%	8
expand_attractor_seeds.py	51	5	90%	6, 42, 97–102
expand_bfs.py	28	1	96%	6
expand_dfs.py	30	1	97%	6
expand_minimal_spaces.py	37	2	95%	6, 31
expand_source_SCCs.py	122	4	97%	14–16, 86, 131
expand_to_target.py	31	3	90%	6, 38, 43
TOTAL	1460	102	93%

Tests	Skipped	Failures	Errors	Time
361	0 :zzz:	0 :x:	0 :fire:	36.863s :stopwatch: