implement input and rework window implementation

moved the window variable as a constant in the window module, and
implement more of GLFW logic, including some basic input handling.

src/io/input.h

@@ -0,0 +1,7 @@
+// Copyright (c) 2025 Quinn
+// Licensed under the MIT Licence. See LICENSE for details
+#pragma once
+#include <GLFW/glfw3.h>
+
+void key_callback(GLFWwindow* win, int key, int scancode, int action, int mods);
+