[BUG] all_paths* methods from differt.rt.graph do not allow from_ to be a keyword argument

[jeertmans]

E.g., DiGraph.all_paths(from_=0, ...) does not work as the text signature (from_) differs from the true signature (from). This is an issue because from cannot be used in Python.

Possible solutions:

• Create a wrapper in Python that maps keyword-arguments to positional arguments.
• Make from_ and others explicitly positional-only parameters.
• Rename from to from_ inside Rust code (at least in the function signatures).