feat: implement Phase 2 RNS carrier

src/client.rs

@@ -66,9 +66,32 @@ pub fn connect(
                 unpinned_static,
             })
         }
-        Scheme::Rns => Err(SmolError::new(
-            "smol+rns:// addresses need the rns feature; rebuild with --features rns",
-        )),
+        Scheme::Rns => {
+            // There is nothing to pin on this carrier (upstream spec 13.4):
+            // the destination hash is the pin, so `require_pin` decides
+            // nothing here and every session is as authenticated as a
+            // pinned TCP one.
+            #[cfg(feature = "rns")]
+            {
+                let _ = require_pin;
+                let destination = addr.destination()?;
+                let transport = crate::rns::transport::RnsTransport::connect(
+                    &destination,
+                    std::time::Duration::from_secs(timeout),
+                )?;
+                Ok(Session {
+                    transport: Box::new(transport),
+                    unpinned_static: None,
+                })
+            }
+            #[cfg(not(feature = "rns"))]
+            {
+                let _ = (addr, require_pin);
+                Err(SmolError::new(
+                    "smol+rns:// addresses need the rns feature; rebuild with --features rns",
+                ))
+            }
+        }
     }
 }