feat(parameters): signal on parameter change

src/Engine/Parameter/Parameter.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "Engine/Parameter/Template.h"
 #include "Engine/Types.h"
+#include <boost/signals2.hpp>
 
 namespace enzo::prm
 {
@@ -11,6 +12,7 @@ public:
     std::string getName() const;
     bt::floatT evalFloat() const;
     void setFloat(bt::floatT value);
+    boost::signals2::signal<void ()> valueChanged;
 private:
     Template template_;
     bt::floatT floatValue_ = 0;