request insights: record local framework spans (1/5) (#93974)
## What
Adds a dev-only local recorder for framework OTEL spans. This lets Next
mirror span data into an in-memory store when local span capture is
enabled, without requiring a user to run an OTEL provider.
Stack:
1. request insights: record local framework spans (1/5) ← current
2. request insights: derive request history and fetch data (2/5)
3. request insights: expose dev snapshots to tools and HMR (3/5)
4. request insights: add agent diagnosis access (4/5)
5. request insights: add DevTools request panel (5/5)
## Review Focus
- Local recorder behavior when no OTEL provider is installed.
- Preserving existing OTEL span API behavior when a provider is
installed.
- Request identity propagation through existing app render async
storage.
## Proof In This PR
- `pnpm jest packages/next/src/server/lib/trace/tracer.test.ts
packages/next/src/server/lib/trace/span-store.test.ts --runInBand`
- `pnpm --filter=next types`
## Deferred Coverage
- Request-level aggregation, fetch enrichment, dev transport, CLI/MCP
access, and the DevTools panel are later PRs in this stack.
<!-- NEXT_JS_LLM_PR -->
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Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
