Keep Lima VSOCK control path working with DHCP on user-v2 links

[jimpudar]

Summary

• Switch the private Lima user-v2 links to DHCP while ignoring DHCP-provided routes, DNS, hostname, MTU, NTP, and timezone data.
• Reserve only the gateway/DNS IP on the user-v2 subnet and keep Rootcell static addressing, DNS, and default routing authoritative.
• Update the user-v2 proof gate and integration coverage to verify the VSOCK restart path and the stricter interface/address invariants.

Testing

• Updated unit coverage for network reservation and proof-gate expectations.
• Added integration coverage for Lima VM restart behavior and post-restart limactl shell access.
• Not run (not requested).