Port the main Next.js E2E test suites to span streaming #23802

Port these E2E test applications to span streaming (12 apps). These are the full Next.js suites: server components, route handlers, middleware and the runtime variants, plus the smaller feature fixtures.

Out of scope, for the record:

• nextjs-15-basepath, nextjs-15-intl, nextjs-16-trailing-slash are the client routing slice, done in test(e2e): Port Next.js routing test apps to span streaming #23797
• nextjs-16-streaming and nextjs-16-streaming-cacheComponents were always streaming
• supabase-nextjs is already ported and uses collectStreamedSpans today
• nextjs-sourcemaps has no tests, nextjs-otlp is errors-only

Apps

Roughly 6,800 lines of specs and 253 waitForTransaction call sites, so this is worth splitting across several PRs rather than one.

What to do

For each app:

1. Remove the traceLifecycle: 'static' pin added in test(e2e): Disable span streaming in e2e test applications #22590 from every Sentry.init (client, server, edge).
2. Rewrite the specs from transaction envelopes to span v2:
   • waitForTransaction becomes waitForStreamedSpan / waitForStreamedSpans
   • event.transaction becomes span.name
   • contexts.trace.op becomes getSpanOp(span) plus span.is_segment
   • contexts.trace.data['x'] becomes span.attributes['x'], which has the shape { value, type }
   • transaction_info.source becomes the sentry.segment.name.source attribute
3. Streamed child spans arrive across several envelopes, so use collectStreamedSpans wherever a test asserts on children of a segment span. These suites assert heavily on server component and route handler children, so this is the bulk of the work.

Client pageload and navigation names carry over when Next resolves the route from its manifest. A pageload on a route the manifest does not know falls back to Pageload, and server-side http.server names go low cardinality.

Reference app: nextjs-16-streaming, which already covers the parameterized case, the fallback case, route handlers and server components.

Keep static trace lifecycle coverage

Before porting this group, duplicate nextjs-16 as-is into nextjs-16-static and leave that copy on the current transaction-based specs. That keeps the static trace lifecycle covered once the rest of the group moves to streaming.

The copy is verbatim; only the app name changes:

• package.json -> name
• start-event-proxy.mjs -> proxyServerName
• every waitForTransaction / waitForError / waitForSession call in tests/

Keep traceLifecycle: 'static' in the copy's Sentry.init calls. The e2e matrix discovers apps by directory, so no CI config change is needed.

nextjs-16 is the largest app in the group at 26 test files, so nextjs-app-dir is a cheaper representative if the copy turns out to be too heavy for CI.