Initial commit: DCNv4 custom op mirror setup

- Add enhanced README with project structure and quick start guide
- Initialize repository with DCNv4 CUDA extension (PyTorch module)
- Include classification, detection, and segmentation subdirectories
- Reference upstream OpenGVLab DCNv4 implementation

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

DCNv4_op/DCNv4/__init__.py

@@ -0,0 +1,2 @@
+from .functions import DCNv4Function, FlashDeformAttnFunction
+from .modules import DCNv4, DCNv4Strip, FlashDeformAttn