Cloud paths should be PathLike

[pjbull]

Lots of Python codebases use os.PathLike to indicate a file that can be read/opened/etc. We want CloudPath to be treated like a path in these instances so that when it is passed to other libraries they call trust its .open() method and work with the file content as expected.

Right now

import os
from pathlib import Path

p = Path("file.txt")
isinstance(p, os.PathLike)  # True

from cloudpathlib import S3Path
s3p = S3Path("s3://bucket/file.txt")
isinstance(s3p, os.PathLike)  # False

In a previous iteration, we had inherited from the PurePath type as below, which I believe made this work. There may be other implementation options as well:

class CloudPath(type(PurePath()):

[jayqi]

This actually looks like it's pretty easy. All we have to do is add an __fspath__ instance method.

https://docs.python.org/3/library/os.html#os.PathLike

>>> class Foo:
...     def __fspath__(self):
...         return ""
... 
>>> foo = Foo()
>>> foo.__fspath__()
''
>>> isinstance(foo, os.PathLike)
True