Fix IPv6 TCP tunnel display formatting (#1980)

Normalize composite tunnel display values before rendering peer and
debug output so IPv6 tunnel types no longer append `6` to the port.

- Preserve prefixes like `txt-` while converting tunnel schemes to
  their IPv6 form.
- Recover malformed values such as `txt-tcp://...:110106` into
  `txt-tcp6://...:11010`.
- Reuse the normalized remote address display in CLI debug output.

easytier/src/instance/dns_server/tests.rs

@@ -232,6 +232,7 @@ async fn test_magic_dns_update_replaces_records_for_same_client() {
         remote_addr: Some(crate::proto::common::Url {
             url: "tcp://127.0.0.1:54321".to_string(),
         }),
+        resolved_remote_addr: None,
     }));
 
     dns_server_inst
@@ -299,6 +300,7 @@ async fn test_magic_dns_update_replaces_records_for_same_client() {
         remote_addr: Some(crate::proto::common::Url {
             url: "tcp://127.0.0.1:54321".to_string(),
         }),
+        resolved_remote_addr: None,
     }));
 
     dns_server_inst