Reorganize headers

include/teqp/models/multifluid.hpp

 #pragma once
 
+#include "json.hpp"
+#include <Eigen/Dense>
+#include <fstream>
 
 template<typename EOSCollection>
 class CorrespondingStatesContribution {

src/multifluid.cpp

 #include "teqp/core.hpp"
-#include <fstream>
-#include <Eigen/Dense>
-
-#include "json.hpp"
 #include "teqp/models/multifluid.hpp"
 
-
 auto build_multifluid_model(const std::vector<std::string>& components) {
     using namespace nlohmann;
     std::string coolprop_root = "C:/Users/ihb/Code/CoolProp";