ScriptExecutionActor previously emitted only an Error 'script' event on failure.
It now also fire-and-forgets an Info 'script' event when execution starts (right
before RunAsync) and when it completes successfully — giving the operational log
the full started/completed/failed lifecycle. Uses the already-resolved
siteEventLogger; fire-and-forget so the event log can never block or fault the
script's own run.
Extends the SingleServiceProvider test helper to also serve IServiceScopeFactory
(returning a self-scope) so ScriptExecutionActor's serviceProvider.CreateScope()
reaches the logging hot path in tests instead of throwing into the catch.
Joseph Doherty
e74c3aef23