fix(tracing-actix-web): populate trace_id at span creation

[tyrypyrking]

PR Type

Bug Fix

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the nightly rustfmt (cargo +nightly fmt).

Overview

When a request arrives with a traceparent header, the trace_id was missing from the "REQUEST START" log entry and only appeared at "REQUEST END". The cause: trace_id was set via span.record() after the span had already been created, but subscribers like tracing-bunyan-formatter emit START during on_new_span — at which point the field is still Empty.

This PR extracts the trace_id from the propagated context before creating the span, so it is baked into the span fields from the start. When there is no remote parent (no traceparent header), the field stays Empty and gets filled later by set_otel_parent exactly as before — no behavior change in that path.

What changed

• tracing-actix-web/src/otel.rs — new extract_trace_id() that pulls the trace_id from request headers via the global propagator.
• tracing-actix-web/src/root_span_macro.rs — root_span! now calls extract_otel_trace_id() before span creation; two inner_span arms handle the "known trace_id" vs "empty" cases (unavoidable since tracing::Value is sealed).

No breaking changes.

Original PR was at the old repo: LukeMathWalker/tracing-actix-web#145

[JohnTitor]

Thanks! LGTM.