Improve Request Insights request and fetch details (#96925)
Stacked on #96924.
## Summary
- Show the sanitized request URL and matched route template, with route
parameters only when the path matches a valid template.
- Distinguish same-origin and external fetches. Truncate long labels
while keeping their full sanitized URL available in tooltips.
- Strip credentials, fragments and query values from displayed URLs and
fetch-span labels.
- Support keyboard trace inspection and contained scrolling, and show
omitted worker-span counts.
## Verification
- 48 focused request, fetch-label and viewer tests passed at this layer.
- The assembled stack passed development tests in both bundlers for
URLs, parameters, origins, keyboard inspection and scrolling.
Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Will Binns-Smith <755844+wbinnssmith@users.noreply.github.com>
