Support VSync callback

src/Library/internal-include/BootLoader/boot_loader.hpp

@@ -8,6 +8,10 @@ namespace JabyEngine {
             void identify();
         }
 
+        namespace Callbacks {
+            void setup();
+        }
+
         namespace CD {
             void setup();
         }

src/Library/internal-include/System/callbacks_internal.hpp

@@ -0,0 +1,21 @@
+#pragma once
+#include <PSX/System/threads.hpp>
+
+namespace JabyEngine {
+    namespace Callback {
+        namespace internal {
+            namespace VSync {
+                static constexpr size_t StackSize = 64;
+
+                extern SysCall::ThreadHandle thread_handle;
+                extern uint32_t              stack[StackSize];
+                void                         routine();
+
+                static void execute() {
+                    MainThread::prepare_if_main(VSync::thread_handle);
+                    Thread::execute_next();
+                }
+            }
+        }
+    }
+}