Improve Textures guide (#2821)

[MinhBDoan]

This PR addresses all requested improvements from issue #2821:

• Reworded "sprite engine" to describe hit box usage
• Added Texture Layers section (Arcade / pyglet / OpenGL)
• Clarified Texture Uniqueness:
  • Defined what "unique" means
  • Explained consequences of duplicate names
  • Explained flipping options
  • Added cross-reference to arcade.load_texture
  • Referenced arcade/cache/texture.py
• Updated Texture Cache section:
  • Clarified name/hash attribute
  • Cross-referenced TextureCache class and flush() method
  • Included example code

[MinhBDoan]

“This PR addresses all requested changes from #2821. First-time contribution, feedback welcome!”