Colima should notify user that vmtype=VZ and arch=x86_64 options should not be used together

### Discussed in https://github.com/abiosoft/colima/discussions/1150

Lima does not allow x86_64 aarchitecture on VZ engine.

```
-> % limactl start --arch x86_64 --vm-type vz
FATA[0001] the YAML is invalid, saved the buffer as "lima.REJECTED.yaml": field `arch` must be "aarch64" for VZ; got "x86_64"
```

But when colima is started with `--arch=x86_64 --vm-type=vz` options, it does not issue any warning or error. Instead it silently falls back to using `qemu` engine on x86_64 architecture.
The `qemu-x86_64` is extremely slow as it does not use Rosetta on mac.

To improve user experience, colima should either

1. Issue a warning that since lima doesn't allow `--arch=x86_64 --vm-type=vz` combination, it is falling back `qemu-x86_64`
2. Throw an error saying `--arch=x86_64 --vm-type=vz` options should not be used together, and do not start the VM.