Fix Request Insights span collection (#95818)
## Summary
Fix Request Insights collection so the dev server records all non-hidden
Next.js spans locally, including non-vanilla trace and wrapped spans,
while preserving the existing OpenTelemetry export allowlist unless
verbose tracing is enabled.
Keep reporting timelines correct by propagating request identity before
work async storage exists, honoring explicit span timestamps, and
anchoring request duration to the BaseServer request span. Standardize
span categories on `next.span_category`, retain presentation-only UI
filtering, and filter internal request identity headers at ingress.
## Verification
- `pnpm test-dev-turbo
test/development/app-dir/request-insights/request-insights.test.ts`
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