MsgAdapter
import type { MsgAdapter } from "https://raw.githubusercontent.com/nats-io/nats.deno/v1.28.2/nats-base-client/internal_mod.ts";
Converts a NATS message into some other type. Implementers are expected to: return [err, null] if the message callback is invoked with an error. return [err, null] if converting the message yielded an error, note that iterators will stop on the error, but callbacks will be presented with the error. return [null, T] if the conversion worked correctly