Restore preservation of leading slashes in FsspecStore.path. The previous fix in #3924 ran path through normalize_path, which is intended for zarr keys and strips leading slashes — corrupting absolute filesystem paths (e.g. /home/foo/data.zarr became home/foo/data.zarr) for backends like LocalFileSystem. FsspecStore now strips trailing slashes only, which still resolves the original path="/" issue without breaking absolute-path callers.