Updates Ship2D (new boss level)

Adds a new boss level to Ship2D (now it has two levels, the previous level with asteroids + a new boss level as a separate scene). By default, the agent trains on both scenes, but the main scene can be changed in Godot editor in case of training only one of the scenes. There are also 2 inference scenes (one for each scene). https://github.com/user-attachments/assets/245e60fe-6a93-42e2-82b9-75cca16c6f5d Some of the other changes: - The agent could previously see asteroids outside of the screen (as long as the raycast hits them), additional invisible walls were added to prevent that, performance might be slightly worse due to this but visually the performance seems decent. - Both the boss scene and asteroid scenes are trained with both player shooting enabled and disabled modes. - Onnx model was updated after retraining the env. - The plugin was updated and the code and the rewards were slightly modified during the update. Todo before merge: - [x] Readme update