Port Next.js client routing E2E test apps to span streaming

[andreiborza]

Port these E2E test applications to span streaming (3 apps).

These three were picked as the first slice because they share one shape: a single test file each, client pageload and navigation route parameterization only, no server-span and no child-span assertions.

Apps

• nextjs-15-basepath
• nextjs-15-intl
• nextjs-16-trailing-slash

What was done

1. Removed the traceLifecycle: 'static' pin added in test(e2e): Disable span streaming in e2e test applications #22590 from instrumentation-client.ts, sentry.server.config.ts and sentry.edge.config.ts. No explicit spanStreamingIntegration() is needed: browserTracingIntegration auto-installs it on the client and ServerRuntimeClient on the server.
2. Rewrote the assertions from transaction envelopes to span v2:
   • waitForTransaction became waitForStreamedSpan
   • event.transaction became span.name
   • contexts.trace.op became getSpanOp(span) plus span.is_segment
   • contexts.trace.data['x'] became span.attributes['x'], which has the shape { value, type }
   • transaction_info.source became the sentry.segment.name.source attribute
3. Renamed routing-basepath-transaction.test.ts to routing-basepath-span.test.ts.

No assertion had to be weakened. Route names carry over unchanged because Next resolves the parameterized route from its manifest before the span starts, so the low-cardinality Pageload fallback never fires for these routes.

PR: #23797

[linear-code]

JS-3500