Persist Request Insights display settings (#96277)
## Summary
- Replaces the per-request verbose checkbox with a global Request
Insights settings menu.
- Persists `requestInsights.verbose` through the existing DevTools
configuration path.
- Restores the setting across reloads.
- Does not include the unrelated global `pagehide` flush behavior.
## Verification
```bash
pnpm build-all
pnpm --filter=next types
pnpm --filter=next build
pnpm test-dev-turbo test/development/app-dir/request-insights/request-insights.test.ts
pnpm test-dev-webpack test/development/app-dir/request-insights/request-insights.test.ts
```
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