[FEATURE] free -h switch request.

### Is your feature request related to a problem? Please describe.

* `free` is built in utility that shows memory usage.
* On platforms with large amounts of memory result of `free` is hard to read, for instance on rPI4B:

```
nsh> free
total used free maxused maxfree nused nfree name
18446744073637310464 2279218446744073637287672 2346418446744073637287672 28 1 Umem
```

### Describe the solution you'd like

Common approach in Unix / POSIX [1] utilities is to use `-h` switch to produce "human readable" output, for instance `df` [2]:

> -h
> The human-readable option selects to format sizes in metric units (e.g. 10 MB). Available in the BSD and GNU coreutils.

[1] https://en.wikipedia.org/wiki/List_of_POSIX_commands
[2] https://en.wikipedia.org/wiki/Df_(Unix)

### Describe alternatives you've considered

_No response_

### Verification

- [x] I have verified before submitting the report.