Implement missing Cube methods

[IceflowRE]

• rotate

  void rotate(const glm::vec3 &axis);

• mirror

  void mirror(const glm::vec3 &axis);

• get_neighbors

  [[nodiscard]] std::array<std::weak_ptr<Cube>, 25> get_neighbors() const;

• get_neighbor

  [[nodiscard]] std::weak_ptr<Cube> get_neighbor(const glm::vec3 &position) const;

• look_at_geometry

  /// Get the cube you were looking at it's geometry.
  [[nodiscard]] std::weak_ptr<Cube> look_at_geometry(const glm::vec3 &position, const glm::vec3 &direction) const;

• point_in_geometry

  /// Gets the smallest existing cube, where the point is inside the geometry.
  [[nodiscard]] std::weak_ptr<Cube> point_in_geometry(const glm::vec3 &position) const;

• point_in_cube

  /// Get the smallest existing cube, where the point is inside the cubes bounding box.
  [[nodiscard]] std::weak_ptr<Cube> point_in_cube(const glm::vec3 &position) const;

• optimize

  /// May merge child cubes into one normal cube if possible.
  void optimize();

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Related:

• Implement a fast ray-octree collision to find selected cubes, cube faces and cube edges. #244

[movabo]

I think we should name the methods in american english because it's the norm. That would mean to name the methods get_neighbor(s) instead of get_neighbour(s).