Address Copilot review: require ipaddr and re-assert the socket port

The guard uses IPAddr but relied on something else loading it first;
require it explicitly. And the rebinding tests lost their port assertion
when the matchers were loosened for newer Net::HTTP keyword args, so
check the port alongside the IP again.

lib/restricted_http/private_network_guard.rb

@@ -1,3 +1,4 @@
+require "ipaddr"
 require "resolv"
 
 module RestrictedHTTP