Remove TTQ debug artifacts

- Remove debug_ttq_model.py (layer inspection script)
- Remove debug_ttq_gradients.py (gradient verification script)
- Remove tests/test_ttq_training.py (local beta config testing)
- Remove bitnet/nn/ttq_linear_pure.py (experimental implementation)

These files were used during TTQ debugging but are no longer needed
now that TTQ training is working correctly.

Author: dariocazzani