Implement lazy loading for models to improve memory usage

[TheSeanLavery]

Problem:

• Loading all models at startup causes high memory usage
• Users with limited VRAM may experience out-of-memory errors
• Slow initial startup time due to loading all models

Solution:

• Implement lazy loading for all models (shape gen, texture gen, background removal)
• Models are now loaded only when needed instead of all at startup
• Each model is loaded on first use and cached for subsequent uses

Benefits:

• Prevents out-of-memory issues on GPUs with limited VRAM
• Faster initial startup time
• More efficient resource usage

Testing:

• Tested on RTX 3090 with successful model loading and generation
• Verified memory usage is significantly reduced during startup
• Confirmed all functionality works as expected with lazy loading