Refactor: Permute systems index offset

[vprusso]

In much the same spirit as https://github.com/vprusso/toqito/issues/145, it would make sense to have a consistent indexing pattern amongst the functions offered in toqito. We should also make this change in the permute_systems.py file as well.

That is, the indexing offset for permute_systems starts at 1 but to be consistent with the rest of the functions (and indeed, to be more intuitive from the perspective of a Python programmer) it should assume an index starting at 0.