Texture lifecycle improvements

[wouterlucas]

This PR introduces several improvements and fixes related to the handling of textures in the rendering pipeline.

• Addressed Texture Reloading Issues: Resolved inconsistencies that occurred when textures transitioned back to a renderable state after being previously marked non-renderable.
• Preserve Source Data: Adjusted the cleanup process to ensure only the GPU texture is cleared when a texture becomes non-renderable, retaining the source data for potential reuse.
• Propagate SubTexture Events: Added functionality to forward SubTexture freed events if the parent texture undergoes cleanup, ensuring proper event handling and lifecycle alignment.
• Introduced comprehensive tests to validate the entire texture lifecycle, ensuring robustness and preventing regressions in future updates. (See screenshot below for test validation details.)