mcookie: Add support for human-readable sizes with the -m option

[alxndrv]

The uutils implementation of mcookie currently doesn't support parsing human-readable sizes provided via the -m option.
We should support units like KiB, MiB etc. like the GNU implementation does.

Relevant code: https://github.com/uutils/util-linux/blob/main/src/uu/mcookie/src/mcookie.rs#L34-L37

[alxndrv]

@sylvestre Opened this as you requested, but don't have permissions to set the label. Mind adding the label for me? 🙏

[sylvestre]

sure, done :)

[quangcito]

I'm taking this up.