chore: clean up emulator types

[dummdidumm]

• the Emulator type is not a class export
• make validated config types more correct by leaving adapter types as optional

Leftovers from #11730, no changeset because the thing is not released yet.
Through this I noticed that export class Server is similarly incorrect; I guess it just doesn't matter really in practise because only adapters use that for their types.

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