chore: checkpoint before Python removal

vendor/tracing/benches/span_fields.rs

@@ -0,0 +1,23 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use tracing::{span, Level};
+
+mod shared;
+
+fn bench(c: &mut Criterion) {
+    shared::for_all_recording(&mut c.benchmark_group("span_fields"), |b| {
+        b.iter(|| {
+            let span = span!(
+                Level::TRACE,
+                "span",
+                foo = "foo",
+                bar = "bar",
+                baz = 3,
+                quuux = tracing::field::debug(0.99)
+            );
+            criterion::black_box(span)
+        })
+    });
+}
+
+criterion_group!(benches, bench);
+criterion_main!(benches);