Remove numpy float64 assumptions from _set_state_transitions so that
it can be re-used with symbolic markov chains
Add a markov method to find states that don't have any outgoing transitions
Fix symbolic markov chain solving for larger matrices
Add some markov methods for detecting absorbing markov chains
Add get_absorbing_probabilities method to markov chains
Share testcases between symbolic and numeric markov chain impelemtations
and fix absorbing markov chain methods for symbolic chains