Add a public measurement-key remapping protocol so callers can safely rename result keys on individual…

Add a public measurement-key remapping protocol so callers can safely rename result keys on individual…: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Today callers have to find and rebuild every measurement themselves, which is especially error-prone for wrapped…