[Bug]: Information set realisation probability for games with absent-mindedness #826
Description
The current implementation of MixedBehaviorProfile computes information set realisation probability by summing the realisation probabilities of its member nodes.
This assumes non-absent-mindedness. For an information set that exhibits absent-mindedness, this "double counts" multiple visits to the information set (and in principle would allow an information set to be visited with probability greater than one!)
We propose that the correct extension of information set realisation probabilities to the case of absent-minded information sets is that it would be the probability the information set is visited at least once. Because node realisation probabilities are retained (and we have the ability to check whether an information set exhibits absent-mindedness) it is possible to compute the realisation structure in more detail if desired.
Currently the information set realisation probability is computed on demand. It would likely make sense to change this to be a cached value for each information set.