Move layout reload policy into platform api

src/layout.h

@@ -1,9 +1,11 @@
 #pragma once
 
+#include <cstdint>
+
 class LayoutManager
 {
     std::string m_path;
-    struct stat m_file_info { 0 };
+    std::int64_t m_file_last_write_time = 0;
 public:
     std::map<uint16_t, std::shared_ptr<class Node>> m_layouts;
     bool m_loaded = false;