restore aggregate-first branch order in shouldTrace

V8 inlines executeField slightly better when the never-taken-on-Node
branch is the trailing fallback rather than an early-returning if body.
The flipped form cost ~5% on introspection; the original ordering plus
c8 ignore start/stop over the Bun-only branch keeps both 100% coverage
and the perf characteristics.

Author: logaretm

src/diagnostics.ts

@@ -150,11 +150,12 @@ export function shouldTrace(
     return false;
   }
   const aggregate = channel.hasSubscribers;
-  /* c8 ignore next 3: Bun-only fallback, exercised by integrationTests/diagnostics-bun. */
-  if (aggregate === undefined) {
-    return SUB_CHANNEL_KEYS.some((key) => channel[key].hasSubscribers === true);
+  /* c8 ignore start: Bun-only fallback, exercised by integrationTests/diagnostics-bun. */
+  if (aggregate !== undefined) {
+    return aggregate;
   }
-  return aggregate;
+  return SUB_CHANNEL_KEYS.some((key) => channel[key].hasSubscribers);
+  /* c8 ignore stop */
 }
 
 /**