provrun.otel

The span names and attributes come from the OpenTelemetry semantic conventions for generative AI, as they stood in release 1.37.0 of the semantic conventions. Those conventions have the status Development, and they have moved to their own repository, open-telemetry/semantic-conventions-genai, which has no release and no schema URL yet. So provrun claims no schema URL, and keeps the names here, in one place, to change them together. When no tracer provider is set, the spans record nothing and cost little.