Improve error message when providing `UPath` instances to `open()`

[ap--]

Currently opening a UPath via open fails with a FileNotFoundError because the URI returned via __fspath__() is just interpreted as a string path.

>>> import upath
>>> pth = upath.UPath("memory:///abc.txt")
>>> pth.write_text("hello world")
11
>>> with open(pth, "rt") as f:
...     print(f.read())
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: 'memory:/abc.txt'

There's two possible ways of improving this error:

1. We raise an exception in non-local UPath subclasses in __fspath__.
2. Or we could keep the basic functionality that fspath returns a string and raise an exception if we detect that the result was used in open

   import os
   
   import sys
   from textwrap import dedent
   from typing import Self
   
   
   class _upath_str(str):
       """helper str subclass for better error messages
   
       This helper class allows us to catch when a user tries
       to provide a UPath instance of a non-local filesystem
       to Python's `open()` function.
       """
       def __str__(self) -> Self:
           return self
   
   
   def _upath_audit_hook(name: str, args: tuple) -> None:
       """audit hook matching the `open` event
   
       Raises a better error message if we detect that a
       user tries to use UPath instances with `open()`.
       """
       if name == "open" and isinstance(args[0], _upath_str):
           msg = dedent(
               f"""\
               builtins.open does not support non-local UPath instances.
                 Use the pathlib interface instead:
                   >>> pth = UPath({args[0]!r})
                   >>> with pth.open() as f:
                   >>>    ...
               """
           )
           raise OSError(msg)
   
   
   sys.addaudithook(_upath_audit_hook)
   
   
   class A:
       def __fspath__(self):
           return _upath_str("abc")
   
       def __str__(self):
           return _upath_str("abc")
   
   a = A()
   b = _upath_str("b")
   print(type(b))
   c = str(a)
   print(type(c))
   print(type(str(c)))
   
   os.fspath(a)
   
   with open(a) as f:
       pass

(1) would be preferable, but (2) might be useful, since there's some code out there that uses __fspath__ to convert os.PathLike to strings.

Need to do a survey of code on github, and if we choose (1) there needs to be a deprecation period.

[ap--]

Correct behavior for this was implemented via #366