Move dag longest path functions to rustworkx-core

[mtreinish]

The dag longest path family of functions:

• dag_longest_path
• dag_longest_path_length
• dag_weighted_longest_path
• dag_weighted_longest_path_length

Are all built using the following rust module:

https://github.com/Qiskit/rustworkx/blob/ab93329be6d8aaccb6c090f4b3ab6f9540ee8114/src/dag_algo/longest_path.rs

and are only exposed via the Python interface currently. We should move these to rustworkx-core so that Rust users can take advantage of them. Realistically probably adding the longest_path module is sufficient as the pyfunctions currently exposed are just an interface layer for Python and don't any extra value for rust consumers.

[henryzou50]

I am interested in this issue. Can you assign this to me?

[mtreinish]

Fixed by #1192