Add dedicated path type throughout the codebase

[ayushjariyal]

issue #6814

In this PR, I introduce a unified PathType alias in aiida/common/types.py to replace inconsistent path-like annotations.
This improves consistency and readability.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.30%. Comparing base (660fec7) to head (0a6e54b).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6819      +/-   ##
==========================================
- Coverage   78.31%   78.30%   -0.01%     
==========================================
  Files         566      567       +1     
  Lines       42762    42771       +9     
==========================================
+ Hits        33484    33486       +2     
- Misses       9278     9285       +7     

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[khsrali]

Thanks @ayushjariyal
Overall looks good!
Please also unify TransportPath with this new path.