`run` doesn't support static IP address assignment

[tofugarden]

Description

The helper supports constraining the DHCP address range on a network using the --start-address, --end-address, and --subnet-mask options. Docs say addresses outside the range are available for static assignment, but run doesn't support assigning a static IP address to a guest - it's DHCP only.

Right now to assign a stable address to a guest, users need DHCP lease reservations in /etc/bootpd.plist. This is an administrative operation that can break other virtual networks (and it's ugly!!).

Proposed solution

Add a --guest-ip-address option to run that sets a static address in the guest's cloud-config.

./run test \
    --start-address 192.168.55.1 \
    --end-address 192.168.55.127 \
    --subnet-mask 255.255.255.0 \
    --guest-ip-address 192.168.55.128

It should in theory be acceptable to only specify the guest IP address (if #258 makes it in, we won't always have DHCP enabled), but for now I think it makes the most sense to require all four options if --guest-ip-address is set so we can validate that nothing silly is being requested.

Potential issues

We don't have a great way to detect address collisions without doing some ARP stuff, which might be a bit complex (but doable). Since this is mostly a development tool, I think this is okay, it's the user's responsibility to ensure the assignment is unique.

[nirs]

I like this - not sure about the name --guest-ip-address.

We don't have any prefix for vm options, so I would keep it just --ip-address. Since this is a development tool, I don't think we have an issue. If this was a tool for user we probably need to make it more clear what is vmnet option and what is vm option. But this is better done by supporting yaml file to describe the vm with some structure.

The command line interface can make this more clear using group of options.

% ./run -h                                 
usage: run [-h] [--connection {fd,socket,runner}] [--operation-mode {shared,bridged,host}] [--start-address START_ADDRESS] [--end-address END_ADDRESS]
           [--subnet-mask SUBNET_MASK] [--network-id NETWORK_ID] [--shared-interface {en8,en0}] [--enable-isolation] [--enable-offloading] [--network NAME]
           [--driver NAME] [--driver-command COMMAND] [--cpus N] [--memory M] [--timeout SECONDS] [--distro {ubuntu,alpine,fedora,debian}] [--dns-servers ADDR]
           [-v]
           vm_name

Run virtual machine using vmnet-helper

positional arguments:
  vm_name               VM name

options:
  -h, --help            show this help message and exit
  --connection {fd,socket,runner}
                        How to connect the helper and vm (fd)
  --operation-mode {shared,bridged,host}
                        vmnet operation mode
  --start-address START_ADDRESS
                        The starting IPv4 address (string) to use for the interface. This address is used as the gateway address. The subsequent address up to
                        and including --end-address_key are placed in the DHCP pool. All other addresses are available for static assignment. The address must
                        be in the private IP range (RFC 1918).
  --end-address END_ADDRESS
                        The DHCP IPv4 range end address (string) to use for the interface. The address must be in the private IP range (RFC 1918).
  --subnet-mask SUBNET_MASK
                        The IPv4 subnet mask (string) to use on the interface.
  --network-id NETWORK_ID
                        The identifier (UUID) of the host network to use on the interface (host operation-mode only).
  --shared-interface {en8,en0}
                        vmnet shared interface for --operation-mode=bridged (en8)
  --enable-isolation    Isolate the guest from other guests on the vmnet interface, requires --operation-mode=host
  --enable-offloading   Enable vmnet tso and checksum-offload options (krunkit driver only)
  --network NAME        Join a network managed by vmnet-broker (macOS 26 only)
  --driver NAME         VM driver (vfkit)
  --driver-command COMMAND
                        Use custom driver command
  --cpus N              Number of vpus (2)
  --memory M            Memory size in MiB (1024)
  --timeout SECONDS     Time to wait for VM IP address (60 seconds)
  --distro {ubuntu,alpine,fedora,debian}
                        Linux distro (ubuntu)
  --dns-servers ADDR    Comma-separated DNS servers for the VM (8.8.8.8,1.1.1.1)
  -v, --verbose         Be more verbose