Rework the path management #111

Currently the path management is tedious, specially in path_op.py.
There are a lot of split(":") and ":" in path and split(".") and "." in path to manage path urn prefixes, and sub-attributes paths.
A Path pydantic model could simplify things here. It could be used in PatchOperation as type of path instead of str.
It should embed the util methods it needs, and be the object to be used in path_op.py methods.
Path may take type parameters.