feat: user definable callback on state transition

include/sta/tacos/statemachine.hpp

@@ -66,6 +66,7 @@
 #include <sta/rtos/event.hpp>
 #include <sta/event.hpp>
 #include <sta/debug/assert.hpp>
+#include <sta/lang.hpp>
 
 #include <functional>
 #include <tuple>
@@ -278,6 +279,18 @@ namespace sta
 			 */
 			std::vector<std::shared_ptr<TacosThread>> threads_[STA_TACOS_NUM_STATES];
 		};
+
+		/**
+		 * @brief Callback that is called when a state transition occurs.
+		 * 
+		 * @param from The state we transitioned from.
+		 * @param to The state we transitioned to.
+		 * @param lockout The lockout time after the transition.
+		 * 
+		 * @ingroup tacos_statemachine
+		 */
+		STA_WEAK
+		void onStateTransition(uint16_t from, uint16_t to, uint32_t lockout){}
 	}  // namespace tacos
 }  // namespace sta