Implement types and validators for Farcaster entities. Types are our own implementation, inspired by the docs we have and by looking into Farcaster API responses.
I picked props that I believe could be somehow useful and can be used as part of the MVP. Added tShapeInexact to allow additional fields that the API can return, but are not needed for us. Validators should only care about things that will be needed for client logic. If I added too many props, we can remove them later to keep the surface as lean as possible, created task for this ENG-11106.