Block fetcher still accepts blocks at or below finalized height

Block fetcher still accepts blocks at or below finalized height: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). After Fast Finality was enabled on BSC, blocks at or below the finalized height are deterministically final — they cannot be reorged out. However, the block…