Since the goal of reading events at the head of the event log is to satisfy a
subscription style interface, there is no point in allowing head polling with
no wait interval. The pagination case already bypasses long polling, so the
extra option is unneessary.
Set a minimum default long-polling interval for the head case.
Add a test for minimum delay.
This allows the caller to stream events. It handles the bookkeeping for cursors
and pagination, and delivers items to a callback.
Handle missed items by reporting a structured error. The caller can use the
Reset method to "catch up" to head after this happens.
Add a manual test CLI to probe a running node. Requires the node to be
configured with the event log settings.
Add a unit test that scripts input to the stream to exercise it.
