feat(gym): apply effort-level reward shaping in the SingleController

[RayenTian]

PR #2770 only wired length-based effort reward shaping into the run_grpo.py (v1) synchronous paths. The SingleController (v2) path runs its own NeMo-Gym rollout via RolloutManager/AsyncNemoGymRolloutImpl, which never applied it.

• Thread EffortLevelsConfig through RolloutManager into AsyncNemoGymRolloutImpl and call the shared _apply_effort_shaping before completions are built, so the shaped reward flows into Completion.reward.
• Fold the effort length/reward metrics into _compute_rollout_metrics.
• setup.py resolves the config via the shared _get_effort_config helper.

No behaviour change when env.nemo_gym.effort_levels is unset (_get_effort_config returns None -> shaping is a no-op).

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