PM-KVQ: Progressive Mixed-precision KV Cache Quantization for Long-CoT LLMs - Liu, Tengxuan; Li, Shiyao; Yang, Jiayi; Zhao, Tianchen; Zhou, Feng; Song, Xiaohui; Dai, Guohao; Yan, Shengen; Yang, Huazhong; Wang, Yu (International Conference on Learning Representations, 2026)