More `dict` and `Path` like api

[LecrisUT]

dict api

• __len__, __iter__, __contains__ Type hints #203
• keys(), values(), items()
  These ones are a bit weird. I propose that these should only contain the items in data since the others can be obtained from the Path api

Path api

• __fspath__
  Probably this one only needs to output posix path as a string
• __truediv__, __rtruediv__, joinpath()
• glob(), rglob()
• iterdir(), walk()
  First part should be trivial, but the latter could use some equivalence: Path.walk()

Non-compliant apis:

• parent (Path api)
  Should always be of type Self. It should return itself if current object is root
• root (Path api)
  Should always be of type str
• get(), __getitem__ (dict api)
  • It should not accept an empty name or a list[str]
  • It should return type equivalent to __getitem__

Other apis

• pop(), setdefault(), __setitem__, etc.
  These are changing the tree structure and should not implemented. If virtual Trees/Path are needed/implemented, these can be added
• unlink(), rmdir()
  Could be implemented, but there is ambiguity if it's a branch defined in main.fmf file