[o11y] Add traceId to user trace

[fhanau]

Builds on #3180. Also see the corresponding upstream PR.

[github-actions]

The generated output of @cloudflare/workers-types has been changed by this PR. If this is intentional, run bazel build //types && rm -rf types/generated-snapshot && cp -r bazel-bin/types/definitions types/generated-snapshot to update the snapshot. Alternatively, you can download the full generated types: https://github.com/cloudflare/workerd/actions/runs/13424781440/artifacts/2620225038

Full Type Diff

diff -r bazel-bin/types/definitions/experimental/index.d.ts types/generated-snapshot/experimental/index.d.ts
2522d2521
<   readonly traceId: string;
diff -r bazel-bin/types/definitions/experimental/index.ts types/generated-snapshot/experimental/index.ts
2534d2533
<   readonly traceId: string;