Behavior for sequencer event consumers.

Defines the contract that all consumers must implement for consumer conformance. Consumers must:

1. Persist cursors in consumer_cursors table
2. Resume from > last_processed_sequence after restart
3. Handle sequence gaps without failure
4. Remain stable during NOTIFY storms
5. Use range-scan for correctness (NOTIFY as wake hint only)
6. Never infer order from timestamps - sequence only

Consumer Implementation Example

defmodule MyApp.EventConsumer do
  use Framework.Sequencer.Consumer

  def handle_events(events) do
    Enum.each(events, &process_event/1)
    :ok
  end

  defp process_event(event) do
    # Process event payload
    :ok
  end
end