feat: allow setting custom topologies in STM

[redeboer]

Closes #96

Made the StateTransitionManager.topologies attribute public, so that it's easier to feed custom topologies to the StateTransitionManager. Note that the topologies attribute is immutable and can only be modified by overwriting it, so I decided to avoid cluttering the code with additional setters and getters.

An example for 2-to-2 topologies (see also #29) is illustrated in a new notebook.

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Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.41%. Comparing base (0de579a) to head (0b7544f).
Report is 143 commits behind head on main.

Files	Patch %	Lines
src/qrules/transition.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #103   +/-   ##
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  Coverage   93.41%   93.41%           
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  Files          15       15           
  Lines        3160     3161    +1     
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+ Hits         2952     2953    +1     
  Misses        208      208           

Flag	Coverage Δ
unittests	93.41% <75.00%> (+<0.01%)	⬆️

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Files	Coverage Δ
src/qrules/transition.py	87.85% <75.00%> (+0.02%)	⬆️