feature request: add `cp` command

Add a `cp` command, based on nodejs cp.

https://nodejs.org/api/fs.html

```
fsPromises.cp(src, dest[, options])
```

with the `recursive` option.

To be compatible with both [ZenFS](https://zenfs.dev/core/) and nodejs.

(Or perhaps lightning-fs is in maintenance mode and so this will not be planned. Still worth asking.)