Separate internal representation of objects

Nobody has claimed this yet.

The gateway often requires additional private information than what is publicly available. For example, GUILD_CREATE requires the guild ID which is why it currently includes separated `id` and `domain` fields, but this should actually only send a `mention` property which means the gateway has to do extra work to get the separated ID itself. Not a huge problem in this specific case, but there will likely be an issue in the future where we want to send special data to the gateway and not to the end user.

So if we extend `consume` and `emitGatewayEvent`'s signatures to be like `payload: GATEWAY_EVENT & {_internal: GATEWAY_PRIVATE}` or something, it'll be easy to remove that data when sending it off?

Start by tracing the `consume` and `emitGatewayEvent` entry points and the current `GUILD_CREATE` payload, especially its separate `id` and `domain` fields. Determine how internal data should be represented and removed before gateway delivery, then verify that public payloads still expose only the intended fields.

Written by the indexing model from the issue text.