add get_expander_port function to AdiPort class

Author: liam-teale

include/pros/devices/port.hpp

@@ -220,6 +220,15 @@ class AdiPort {
         return m_index;
     }
 
+    /**
+     * @brief Get the smart port of the ADI expander
+     *
+     * @return constexpr SmartPort
+     */
+    constexpr SmartPort get_expander_port() const {
+        return m_expander_port;
+    }
+
     /**
      * @brief Get the mutex for the given port
      *