feat: 为 Python worker 输出添加行前缀，并启用无缓冲模式

- 新增 prefixWriter，对每行输出添加 [python:N] 前缀，便于与 Go 日志区分
- 注入 PYTHONUNBUFFERED=1，确保 print() 实时输出不被管道缓冲

worker.go

@@ -60,18 +60,20 @@ func (w *worker) start() error {
 		fmt.Sprintf("GOBRIDGE_WORKER_ID=%d", w.id),
 		fmt.Sprintf("GOBRIDGE_WORKER_COUNT=%d", w.cfg.workers),
 		"GOBRIDGE_DEATH_FD=3", // ExtraFiles[0] → fd 3
+		"PYTHONUNBUFFERED=1",  // Python stdout/stderr 不缓冲，print() 立即输出
 	)
 	cmd.ExtraFiles = []*os.File{pr} // fd 3 in child
-	if w.cfg.stdout != nil {
-		cmd.Stdout = w.cfg.stdout
-	} else {
-		cmd.Stdout = os.Stdout
+	prefix := fmt.Sprintf("[python:%d] ", w.id)
+	stdout := w.cfg.stdout
+	if stdout == nil {
+		stdout = os.Stdout
 	}
-	if w.cfg.stderr != nil {
-		cmd.Stderr = w.cfg.stderr
-	} else {
-		cmd.Stderr = os.Stderr
+	stderr := w.cfg.stderr
+	if stderr == nil {
+		stderr = os.Stderr
 	}
+	cmd.Stdout = newPrefixWriter(stdout, prefix)
+	cmd.Stderr = newPrefixWriter(stderr, prefix)
 
 	if err := cmd.Start(); err != nil {
 		pr.Close()