feat: force GPU usage with device_map to prevent CPU memory overflow

[Erlonidas]

Problem

The original implementation was not properly utilizing GPU when available, causing the model to load on CPU RAM instead. This resulted in:

• CPU RAM overflow: Maxing out 12GB system RAM
• GPU underutilization: GPU sitting idle at 0GB usage despite being available
• Significantly slower processing: Without GPU acceleration

Solution

This PR forces the model to load directly on GPU using device_map="cuda:0", ensuring proper GPU utilization from the start.

Changes

• Load model directly on GPU with device_map="cuda:0" parameter
• Add informative message showing GPU device name on startup
• Use torch_dtype=torch.bfloat16 for optimized memory usage
• Maintain CPU fallback for systems without GPU
• Move device detection before model loading

Benefits

• Prevents CPU RAM overflow: Model loads on GPU VRAM (~9GB) instead of system RAM
• Better performance: Tested with 70 PDF pages processed in 2h40min with GPU vs much slower on CPU
• Automatic GPU detection: No manual configuration needed
• Memory efficient: Uses bfloat16 precision on GPU
• User-friendly: Shows which GPU is being used at startup

Testing

Tested on Google Colab with Tesla T4 GPU (15GB VRAM):

• ✅ Model successfully loads on GPU (~9GB VRAM usage)
• ✅ CPU RAM stays low (~3GB instead of maxing out at 12GB)
• ✅ 70 PDF pages processed successfully in 2h40min
• ✅ Proper GPU utilization throughout processing

Before vs After

Before:

• CPU RAM: 12.7GB / 12.7GB (maxed out) ❌
• GPU VRAM: 0.0GB / 15.0GB (unused) ❌

After:

• CPU RAM: ~3GB / 12.7GB (normal) ✅
• GPU VRAM: ~9GB / 15.0GB (properly utilized) ✅