Feature request: built-in base64 string validator

Feature request: built-in base64 string validator: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I'm using Zod to validate API payloads, and a few of my endpoints accept fields that are expected to be base64-encoded strings (think things like binary blobs…

The task

I'm using Zod to validate API payloads, and a few of my endpoints accept fields that are expected to be base64-encoded strings (think things like binary blobs uploaded as base64, signed tokens, webhook payloads, etc.).

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.