Represents a namespace package's path.
It uses the module *name* to find its parent module, and from there it looks
up the parent's __path__. When this changes, the module's own path is
recomputed, using *path_finder*. The initial value is set to *path*.
For top-level modules, the parent module's path is sys.path.
*path_finder* should be a callable with the same signature as
MetaPathFinder.find_spec((fullname, path, target=None) -> spec).