UTM handles VM on external volume poorly if volume is unplugged

**Describe the issue**
UTM flooded the host so rapidly with alerts to the point that I was unable even to force quit UTM as a result of accidentally disconnecting the external volume where the VM is located. I had to forcibly restart the entire host in order to use the system.

Naturally, I don't expect this to go well when the VM disk suddenly ceases to exist during operation, but I would appreciate if it was possible to provide the user an opportunity to reconnect the external volume if at all possible, or even automatically kill the affected VM if not.

**Configuration**
* UTM Version: 4.6.4 (107)
* macOS Version: 15.7
* Mac Chip (Intel, M1, ...): M3 Pro