feat: add Cosmos3-Nano quantization support
- Fix is_diffusion_model() to skip model_index.json for cosmos3_omni
- Add loading path in mllm_load_model() for Cosmos3
- Register multimodal block handler in SPECIAL_MULTIMODAL_BLOCK
- Add cosmos3_omni to SUPPORT_ONLY_TEXT_MODELS
- Register calibration template
- Fix revert_checkpoint_conversion_mapping regex (don't strip capturing groups)
- Add integration analysis doc
