pass denoising step info to cache hooks via cache_context
Replaces SeaCache's pipeline-state callbacks: the pipeline attaches the loop
coordinates (step_index, sigma, num_inference_steps) to the denoiser call with
`cache_context(name, ...)`, carried by a frozen CacheContext dataclass and stored
on each stateful hook's StateManager (the registry no longer holds context).
Co-Authored-By: Dhruv Nair <dhruv.nair@gmail.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
