Bug in xopen with Windows pathnames
Currently, `xopen` function has a bug with local Windows pathnames:

From its implementation:
```python
def xopen(file: str, mode="r", *args, **kwargs):
    file = _as_posix(PurePath(file))
    main_hop, *rest_hops = file.split("::")
    if is_local_path(main_hop):
        return open(file, mode, *args, **kwargs)
```

On a Windows machine, if we pass the argument:
```python
xopen("C:\\Users\\USERNAME\\filename.txt")
```
it returns
```python
open("C:/Users/USERNAME/filename.txt")
```