Side-effect orchestration for dispatch events — extracted from the prior AshDispatch.Changes.DispatchEvent module.

Why this exists separately from the notifier

AshDispatch.Notifier is a thin adapter that pattern-matches the notification's action and looks up per-action config. The actual dispatch logic — event-module resolution, context building, channel resolution, dispatcher invocation — lives here. This isolates the "what to dispatch" decisions (Notifier) from the "how to dispatch" orchestration (DispatchHandler).

Two modes (preserved verbatim from the prior change module)

• DSL-based — driven by an event :foo, ... end block that the transformer persisted as a config map with :event_config.
• Standalone — for events that bypass the DSL block and were historically registered via change DispatchEvent, event_id, data_key. Mosis has zero such callers today; the path is preserved for AshDispatch substrate completeness.