feat: emit warning for req.closed only once

Author: mmarchini

lib/request.js

@@ -2,7 +2,7 @@
 
 'use strict';
 
-const { emitWarning } = require('node:process');
+const { emitWarning } = require('process');
 var url = require('url');
 var sprintf = require('util').format;
 
@@ -846,12 +846,16 @@ function patch(Request) {
      * @function closed
      * @returns {Boolean} is closed
      */
+    let closedDeprecatedWarned = false;
     Request.prototype.closed = function closed() {
-        emitWarning(
-            'restify req.closed is deprecated, will be removed on Restify 10',
-            'RestifyDeprecationWarning',
-            'RestifyDEPReqClosed'
-        );
+        if (!closedDeprecatedWarned) {
+            emitWarning(
+                'restify req.closed is deprecated, will be removed on v10',
+                'RestifyDeprecationWarning',
+                'RestifyDEPReqClosed'
+            );
+            closedDeprecatedWarned = true;
+        }
         var self = this;
         return self.connectionState() === 'close';
     };