CSPDarknet-53 backbone — Darknet-53 (YOLOv3 base) with CSP wrap.

The CSPNet recipe applied to the Darknet-53 trunk (Wang et al., CVPRW 2020); same architecture later adopted by YOLOv4. Returns the final feature map only; pair with a classifier head via cspdarknet_53_cls.

Reference: Wang et al., "CSPNet: A New Backbone that can Enhance Learning Capability of CNN", CVPRW 2020 (arXiv:1911.11929).