refactor: move task_fn into its own crate

benches/patterns/breakdown.rs

@@ -1,7 +1,8 @@
 //! 10,000 task breakdown benchmarks - construction vs execution
 
 use criterion::{BatchSize, Criterion};
-use dagx::{task_fn, DagRunner};
+use dagx::DagRunner;
+use dagx_test::task_fn;
 
 pub fn bench_10k_breakdown(c: &mut Criterion) {
     let rt = tokio::runtime::Runtime::new().unwrap();

benches/patterns/diamond.rs

@@ -1,8 +1,8 @@
 //! Diamond pattern benchmarks (fan-out then fan-in)
 
 use criterion::Criterion;
-use dagx::{task_fn, DagRunner, TaskHandle};
-
+use dagx::{DagRunner, TaskHandle};
+use dagx_test::task_fn;
 pub fn bench_diamond(c: &mut Criterion) {
     let rt = tokio::runtime::Runtime::new().unwrap();
 

benches/patterns/fanout.rs

@@ -1,8 +1,8 @@
 //! Fan-out pattern benchmarks (1 → N dependencies)
 
 use criterion::Criterion;
-use dagx::{task_fn, DagRunner, TaskHandle};
-
+use dagx::{DagRunner, TaskHandle};
+use dagx_test::task_fn;
 pub fn bench_fanout(c: &mut Criterion) {
     let rt = tokio::runtime::Runtime::new().unwrap();