dsh-large-proj-perf: Eliminating blocking caused by fork, history loading, and disk spilling in DSH super large sessions

**Preface** The design philosophy of DSH (DeepSeek Harness) is "everything is a plugin." Several performance-oriented plugins already exist in the community: @linxin666/dsh-perf handles observability and frontend rendering load reduction, while dsh-pref-kit performs streaming incremental merging at the source. However, there is a class of issues regarding large existing sessions that these plugins cannot address: once the number of events in a single session accumulates to several hundred thousand, forking sub-sessions, reopening historical sessions, and persisting fork results to disk all become synchronous heavy tasks on the event loop—causing anything from a few hundred milliseconds of lag to a single core running at full capacity for 20 minutes, or even a direct RangeError. This article introduces dsh-large-proj-perf (v1.2.0, MIT license, author orangeofc).