Provide a better way to allow static type-narrowing for the UPath constructor

[ap--]

Currently it seems all python type-checkers seem to have some limitation regarding either __new__ overloads or type.__call__ overloads.

see: #435

This issue tracks if we can come up with a better way to overload the constructor thats supported by all typecheckers.

xref / blocked-by:

• astral-sh/ty#281
• python/mypy#15182
• python/mypy#17251

[ap--]

There are two ways right now to get IDE autocompletion and suggestions for storage_options:

1. use the correct upath subclass directly

2. use upath.registry.get_upath_class to narrow to the right class on protocol