MatryoshkaKV: Adaptive KV Compression via Trainable Orthogonal Projection - Lin, Bokai; Zeng, Zihao; Xiao, Zipeng; Kou, Siqi; Hou, TianQi; Gao, Xiaofeng; Zhang, Hao; Deng, Zhijie (International Conference on Learning Representations, 2025)