Support for Disk/Memory Units Other Than GiB for --memory and --disk flags

### Description

Currently, the `--memory` or `--disk` flags allow users to specify the amount of memory allocated to the VM in Gibibyte (GiB).

Are there plans for Colima to support other units for CPU/Disk/MEM allocation, specifically Mebibyte (MiB)?

## Suggestion 1

```bash
colima start --memory 2GiB
colima start --memory 512MiB
```

This change would provide flexibility to the users and make it easier to manage memory resources.

## Suggestion 2

Alternatively, Colima can also support `float` (instead of only `int`) values for memory allocation. This would allow users to specify the exact amount of memory they want to allocate while keeping the unit as GiB.

Here is an example of how this could look:
```
colima start --memory 0.5 --disk 0.5 # GiB
```