Several scaffolds that pre-date the runner refactor still pointed at
removed APIs:
* ``EvalResult`` (and its ``Evaluator.evaluate_dataset`` docstring)
exposed a class that is never returned anywhere; drop it from the
public API.
* ``Evaluator``'s module docstring still referenced the removed
``EvalRunner`` layer; trim to the current Evaluator → EvalWorker
shape.
* ``WM_EVAL_CACHE`` survived as a fallback env var from the wm-eval
port; remove and keep only ``FASTVIDEO_EVAL_CACHE``.
* The contributor docs documented ``batch_unit`` and
``trial_forward``/``Evaluator.calibrate()`` which were dropped from
``BaseMetric`` in earlier refactors; update to the current contract.
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