Fix issues for using NWM

[SorooshMani-NOAA]

• After adding cache files for NWM, the default object type conversion runs into an issue for PathLike type.
• The docstring was missing from the NWM configuration class definition

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.84%. Comparing base (25a599e) to head (da42960). Report is 61 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #152 +/- ## ======================================= Coverage 64.84% 64.84% ======================================= Files 35 35 Lines 3871 3871 ======================================= Hits 2510 2510 Misses 1361 1361 ```

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