Only create Nitro storage spans when there is a parent span #25803

The Nitro storage integration creates cache spans (with db.* attributes) when there is no active span. Each of these spans becomes its own root span and has no context.

Pass requiresParentSpan: true to bindTracingChannelToSpan in packages/server-utils/src/integrations/nitro/captureStorageEvents.ts.

Add a test that checks that an operation without an active span creates no span.