Disconnect without resetting YubiKeys if it is safe to do so

This enables the PIN caches to be preserved across age-plugin-yubikey
processes, allowing PIN policies of "once" to become meaningful.

src/plugin.rs

@@ -249,6 +249,8 @@ impl IdentityPluginV1 for IdentityPlugin {
                     }
                 }
             }
+
+            conn.disconnect_without_reset();
         }
         Ok(file_keys)
     }