Calls to NewPath from other functions like Glob() and Parent() reset the separator to the os default/don'r preserve path opts

[lmvlmv]

When calling some of the methods like Glob() or Parent() on an pathlib.Path with a non-os matching separator defined, they can result in a call to NewPath() which defaults to the os.PathSeparator value

// NewPath returns a new OS path
func NewPath(path string, opts ...PathOpts) *Path {
	p := &Path{
		path:            path,
		fs:              afero.NewOsFs(),
		DefaultFileMode: DefaultFileMode,
		DefaultDirMode:  DefaultDirMode,
		Sep:             string(os.PathSeparator),
	}
	for _, opt := range opts {
		opt(p)
	}
	return p
}

I'm writing tests that operate on an afero in-memoryFS and am passing Path objects with the separator set to "/". Running the tests/code on a Windows machine gives unstable results as the calls keep resetting the separator to "\".

e.g.

fs := afero.NewMemMapFs()
fs.Create("testdata/main")
principal := pathlib.NewPath("testdata/main", pathlib.PathWithAfero(*fs), pathlib.PathWithSeperator("/"))
parent := principal.Parent()
fmt.Printf("Parent sep: %s\n", parent.Sep)

gives

principal sep: /
Parent sep: \

I'm new to golang and porting some code I have in python over using this library and that code needs to be multi-platform. Testing could happen on any OS.

Afero seems to handle both \ and / as valid separators, but as I'm checking correctness of the returned path the conversion the os dependent separator makes that tricky.

Seems they all visit this call:

// NewPathAfero returns a Path object with the given Afero object
//
// Deprecated: Use the PathWithAfero option in Newpath instead.
func NewPathAfero(path string, fs afero.Fs) *Path {
	return NewPath(path, PathWithAfero(fs))
}

Perhaps calls to NewPath in the utility methods could preserve the path options of the path object, unless the call needs to modify them?