Enforce schema when using json writer() or json reader()

Enforce schema when using json writer() or json reader(): a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Hi, I have reproduced the example in https://fastavro.readthedocs.io/en/latest/json writer.html but I've changed some items of the records array in order to introduce…