Camera: Add optimized screenPointToRay(Vector2f) for efficient raycasting

[capdevon]

This PR introduces a new public method, screenPointToRay(Vector2f click2d), to the Camera class. This method provides a highly efficient way to generate a picking Ray in world coordinates from a given 2D screen coordinate.

Motivation:

The ability to accurately and efficiently convert a 2D screen point (e.g., from a mouse click) into a 3D ray in world space is fundamental for various interactive features, such as:

• Object Picking: Determining which 3D object a user has clicked on.
• Raycasting: Performing intersections with geometry for game logic (e.g., shooting, selection).
• Gizmo Manipulation: Interacting with 3D manipulation tools.

See https://docs.unity3d.com/6000.1/Documentation/ScriptReference/Camera.ScreenPointToRay.html

usage example:

Ray pickingRay = cam.screenPointToRay(inputManager.getCursorPosition());

// Now 'pickingRay' can be used for intersection tests with 3D objects
// e.g., pickingRay.intersects(someSpatial.getWorldBound());

Edit:
add TestMousePick