Reachability method with less overhead

[daemontus]

This PR introduces a better reachability algorithm which uses structural information about the BN to eliminate certain transition checks and thus reduces overhead.

This is mostly a "constant factor" improvement, and in certain edge cases can be even slower (produces slightly larger BDDs), but overall seems to be worth it:

ID	Basic	Structural
002	DNF	DNF
004	DNF	DNF
012	28s	12s
016	27s	9s
019	1.5s	0.3s
039	141s	222s
050	2154s	1843s
051	8s	7s
059	0.7s	1.4s
078	8783s	2477s
079	DNF	DNF
080	35s	14s
082	DNF	DNF
083	DNF	DNF
092	9s	6s
143	1.5s	0.5s
148	4s	2s
151	2314s	307s
160	24s	4s
179	4s	1s
192	DNF	DNF
195	DNF	DNF
204	34s	13s
207	4s	2s
209	DNF	DNF
210	DNF	DNF
211	DNF	DNF
220	DNF	DNF
222	DNF	DNF
223	213s	4s
224	5s	3s

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (2503d58) 80.36% compared to head (27c3442) 80.42%.

Files	Patch %	Lines
src/symbolic_async_graph/reachability.rs	89.04%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #55      +/-   ##
==========================================
+ Coverage   80.36%   80.42%   +0.06%     
==========================================
  Files          71       72       +1     
  Lines        4827     4890      +63     
==========================================
+ Hits         3879     3933      +54     
- Misses        948      957       +9     

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