feature: broader path-like support

[wpbonelli]

Is your feature request related to a problem? Please describe.
FloPy currently expects strings for some path parameters (files/dirs to read from or write to, etc). #1712 recently added support for pathlib.Path to some internals, allowing path-like objects to be passed e.g. to MFSimulation's ctor.

Describe the solution you'd like
Extending path-like support to all user-facing APIs would be convenient for use with modern pathlib.Path, removing the need to wrap with str(...), without breaking existing string usages. Type hint Union[str, os.PathLike] could be used in the spirit of PEP 519 — further SO discussions here and here. In many cases Path/path-like are already implicitly supported and docstrings could just be updated, but this is not universally true and some refactoring would be needed.

[mwtoews]

Thanks for raising this. I've been slowly working on this since October 2022, e.g. #1583, #1603. With some of the previous refactoring, I've generally found path manipulation with pathlib to be simpler and easier to read than os.path.

Some general tips:

• Refer to the handy table of comparison between pathlib and os module functions
• Docstrings that have (e.g.) "file_name : str" should be changed to "file_name : str or PathLike"
• If parameter checks are done with the file/path variable, use e.g. if isinstance(file_name, os.PathLike), because there are other path-like classes e.g. path
• Update tests to that use refactored functions that use both str and PathLike names, to maintain coverage/support for both

[wpbonelli]

Closed by #1730. Some notebooks and tests still use strings instead of paths, but maybe not a terrible idea to keep it that way to exercise both options