cli: add local route-table fallback for public IP detection

[ben-dz]

Resolves: #2962

Summary of Changes

• Add is_public_ipv4() that rejects all IANA-reserved, private, loopback, link-local, CGNAT, documentation/test, multicast, and reserved ranges — equivalent to nightly
  Ipv4Addr::is_global()
• Add local route-table fallback (get_public_ipv4_via_route()) so public IP detection works when ifconfig.me is unreachable
• Refactor get_public_ipv4() to try HTTP first, then fall back to the routing-table approach with the new address validation

Testing Verification

• Comprehensive unit tests covering every rejected range with boundary checks (just-below and just-above each CIDR block)
• rust-test, rust-build, rust-lint all passing in CI