refactor: split into static libraries and restructure scenes

- Create cbt_opengl static library for OpenGL abstraction
- Create cbt_scene static library for base scene class
- Create scenes_cube static library for cube scene
- Move scene base to cbt/ (utility), scenes to root scenes/
- Link libraries in dependency chain: cuber -> scenes -> cbt_scene -> cbt_opengl

cbt/scene.cpp

@@ -0,0 +1,13 @@
+#include "cbt/scene.hpp"
+
+namespace cbt {
+
+auto scene::init() -> bool {
+    return true;
+}
+
+auto scene::update(float) -> void {}
+
+auto scene::render() -> void {}
+
+}

cbt/scene.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <chrono>
+
+namespace cbt {
+
+class scene {
+public:
+    virtual ~scene() = default;
+
+    virtual auto init() -> bool;
+    virtual auto update(float delta_time) -> void;
+    virtual auto render() -> void;
+};
+
+}