Investigate moving determine_alternative_permissible_values function for genes to __init__ of Genome.

[mschmidt87]

In the implementation introduced in #180 , we check for alternative permissible values for each gene every time we call the mutate method. This is wasteful since we can just do this once in the __init__ of Genome and store the results in a data structure.

This ticket is therefore about investigating this and implementing the change if deemed feasible.

[HenrikMettler]

As a side note: We can not directly initialize the alternative permissible value, but only all permissible values for a gene, since the former depends on the current allele (basically: alternative_permissible_values = all_permissible_values \ {current_value})

[jakobj]

for completeness i'm quoting from #180

this might save quite some computation time at the expense of increased memory usage and slower instantiation of Genome objects. as always, the root of all evil is premature optimization, so i wouldn't implement this without profiling and finding that this is indeed a bottleneck. maybe a more lightweight compromise would be some kind of memoization, e.g., decorating the function determining all permissible values with the lru cache decorator.

[mschmidt87]

Given that the memory footprint of the data structure to be stored is probably very small, and that the function determining all permissible value is always called with the same argument (the configuration of the dna, if it it determine all permissible value as suggested by @HenrikMettler above), I think that memoization is not a good alternative.