support for str instead of Path

[veenstrajelmer]

Is your feature request related to a problem? Please describe.
Currently, it is necessary to import Path whenever using hydrolib functions: from pathlib import Path

Describe the solution you'd like
This is acceptable, but I can imagine it would be fairly easy to add support for plain strings also, by converting all strings to Path(str) in hydrolib. This saves a bit of a hassle. At least, if chosen not to add support, I would suggest to raise a more explanatory error than this:
AttributeError: 'str' object has no attribute 'is_absolute'

Instead, explicitly informing the user to wrap Path() around the provided string.

[MRVermeulenDeltares]

in the FileModel class, the filepath variable can have a check on the input for path.
in the FileModel class, the save method can have a check on the input for path.
in the FileModel class, the constructor can have a check on the input for path.
Classes inheriting from the FileModel will have the path input resolved via the parent class.
e.g. the DIMR class inherits from the ParsableFileModel which in turn inherits from FileModel.