vLLM v0.29.0 makes Model Runner V2 the default and adds Mamba prefix caching

vLLM v0.29.0 (Sept 9, 594 commits from 277 contributors) makes Model Runner V2 the default for all models, adds new model support (Qwen3.8-Flash-Next, Kimi K3 NVFP4, NemotronH_Omni_Reasoning_V3, GraniteSWA), and upgrades speculative decoding with per-request acceptance stats and adaptive logprob verification. Mamba prefix caching lands with a 9-25% TTFT improvement. Breaking: ten deprecated architectures removed, PyAV decoder removed, and 'vllm serve' replaces python -m vllm.entrypoints.openai.api_server.