Default in-memory persistence adapter using ETS.

Survives worker restarts within the same VM but not VM restarts. The GenServer owns the ETS tables, while Store callbacks operate on the :public tables directly for zero-overhead reads and writes.

When the Runner is started without an explicit :store, it will start this ETS store automatically. If you configure store: Runic.Runner.Store.ETS explicitly, start this module in your supervision tree before the Runner.

Stream Semantics

Supports event-sourced append/3 and stream/2 via a second :ordered_set ETS table keyed by {workflow_id, sequence}. A counter table tracks the next sequence number per workflow.