Pure in-memory adapter storing threads in a map.
No external processes - state is carried in adapter_state. Thread is auto-created on append if it doesn't exist.
Delete a thread
List all thread IDs
@spec delete(%{threads: map()}, String.t()) :: {:ok, %{threads: map()}}
@spec list(%{threads: map()}) :: {:ok, %{threads: map()}, [String.t()]}