REF: Replace os.path with pathlib.Path in pandas_web.py

[iabhi4]

Replaces os.path with pathlib.Path in pandas_web.py, as suggested by @datapythonista in 61578. No functional changes, verified site generation remains correct

• Ran pre-commit check

[datapythonista]

Looks good, but we need to make everything that is a path a pathlib object when it's first created. Not create it as a string and cast it for every operation.

[iabhi4]

Thanks for the review! updated to make sure all paths are created as Path early and used consistently. Removed redundant casts too.