FS emulates fs.FS. Note: the path (map key) cannot begin with "/"!
type FS map[string]*File
func (f FS) Open(name string) (fs.File, error)
Open implements the same method as documented on fs.FS, except it doesn't validate the path.
type File struct{ CloseErr error }
func (f *File) Close() error
func (f *File) Read(_ []byte) (int, error)
func (f *File) Seek(_ int64, _ int) (int64, error)
func (f *File) Stat() (fs.FileInfo, error)