7. A core owns its pipeline

Context. The simulator held pipelines: Vec<PipelineDispatch> beside state.cores: Vec<Core>, two vectors related only by index.

Decision. Core is the per-core model: units: CoreUnits (caches, MMU, write-combining buffer, branch predictor) and pipeline: PipelineDispatch. SystemState::pipeline_ctx hands out the pipeline together with a CoreCtx built from disjoint borrows of the hart, the units and the uncore. Pipelines are built with the state and pointed at the loaded PC when the Simulator is created.

Consequences. There is one per-core collection, indexed by CoreId. The context types refer to CoreUnits, so a pipeline cannot reach another pipeline, or its own, through its context.