LocalStore fsspec adding extra path stuff in Windows

[amachanic]

from obstore.fsspec import FsspecStore
fs = FsspecStore('file')
fs.exists('c:/temp/xx.txt')

-->

Generic LocalFileSystem error: Unable to walk dir: IO error for operation on C:\C:\temp\xx.txt: The filename, directory name, or volume label syntax is incorrect. (os error 123)

Debug source:
Generic {
    store: "LocalFileSystem",
    source: UnableToWalkDir {
        source: Error {
            depth: 0,
            inner: Io {
                path: Some(
                    "C:\\C:\\temp\\xx.txt",
                ),
                err: Os {
                    code: 123,
                    kind: InvalidFilename,
                    message: "The filename, directory name, or volume label syntax is incorrect.",
                },
            },
        },
    },
}

More info in #555

Note: I am happy to try to fix this and maybe some other fsspec bugs myself. (I'm not yet aware of what those might be, but once this is fixed I'll be able to find out more as I try to get obstore working for my use case.) However, I can't find any contribution guidelines. LMK if there's some kind of readme on that topic, or what info I need to get going as a contributor if you're open to external help. Thanks.

[kylebarron]

The fsspec adapter is best-effort. I'm not putting any time into it myself, but I'm happy to review PRs for it.

The contributor documentation is in https://github.com/developmentseed/obstore/blob/main/DEVELOP.md