doc(examples): add tracing example with Chrome Trace Event output

- add examples/tracing/tracing.go demonstrating WithTracer() usage
- pipeline: fetch/load (parallel) -> process (subflow) -> output
- output JSON can be visualized in chrome://tracing or Perfetto UI

Author: noneback

examples/tracing/tracing.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"runtime"
+	"time"
+
+	gotaskflow "github.com/noneback/go-taskflow"
+)
+
+// This example demonstrates how to capture Chrome Trace Event data
+// using WithTracer(). The output can be visualized in chrome://tracing
+// or Perfetto UI (https://ui.perfetto.dev/).
+func main() {
+	executor := gotaskflow.NewExecutor(uint(runtime.NumCPU()*4), gotaskflow.WithTracer())
+
+	tf := gotaskflow.NewTaskFlow("tracing-demo")
+
+	// Stage 1: parallel fetch and load
+	fetch := tf.NewTask("fetch", func() {
+		fmt.Println("fetch")
+		time.Sleep(10 * time.Millisecond)
+	})
+	load := tf.NewTask("load", func() {
+		fmt.Println("load")
+		time.Sleep(8 * time.Millisecond)
+	})
+
+	// Stage 2: process depends on both fetch and load
+	process := tf.NewSubflow("process", func(sf *gotaskflow.Subflow) {
+		transform := sf.NewTask("transform", func() {
+			fmt.Println("transform")
+			time.Sleep(5 * time.Millisecond)
+		})
+		enrich := sf.NewTask("enrich", func() {
+			fmt.Println("enrich")
+			time.Sleep(4 * time.Millisecond)
+		})
+		transform.Precede(enrich)
+	})
+
+	// Stage 3: output waits for process to complete
+	output := tf.NewTask("output", func() {
+		fmt.Println("output")
+		time.Sleep(3 * time.Millisecond)
+	})
+
+	fetch.Precede(process)
+	load.Precede(process)
+	process.Precede(output)
+
+	executor.Run(tf).Wait()
+
+	fmt.Println("--- Chrome Trace JSON (open in chrome://tracing or https://ui.perfetto.dev) ---")
+	if err := executor.Trace(os.Stdout); err != nil {
+		log.Fatal(err)
+	}
+}