Add `parent` as a detection method

[archiif]

This detection method simply sets the current working directory to the parent directory of the current file. Useful as a fallback when you are dealing with simple and generic projects that lsp and pattern can't meaningfully detect. Also, the parent directory regex originally ended up producing results such as C: or D: on Windows, which fs_scandir for some reason interprets as the current working directory. So to fix that, the new regex will always produce paths that ends with a / when it successfully finds a parent directory.