Expand the worker1 'exec' op handling for per-row callbacks for API-level consistency...

Expand the worker1 'exec' op handling for per-row callbacks for API-level consistency and smooth some edges between worker1 core and worker1-promiser. Add worker1 'config-get' message to fetch the serializable parts of the sqlite3.config state. Improve the 'open' op's handling of the 'persistent' option (noting that we cannot yet test that case from a worker).

FossilOrigin-Name: 509f8839201ec1ea4863bd31493e6c29a0721ca6340755bb96656b828758fea7