In-memory artifact store backed by an Agent process.

Artifacts are stored in a nested map keyed by {app_name, user_id, session_id, filename} with a list of versions (newest first).

Usage

{:ok, pid} = ADK.Artifact.InMemory.start_link()
runner = ADK.Runner.new(app_name: "app", agent: agent, artifact_service: {ADK.Artifact.InMemory, pid: pid})