chore(ci): update Xcode to 16.4.0 on M4 Pro resource class

Migrate from deprecated M1 (macos.m1.medium.gen1) to M4 Pro
(m4pro.medium) and update Xcode from 15.4.0 to 16.4.0.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dnl-moh

.circleci/config.yml

@@ -6,8 +6,8 @@ orbs:
 executors:
   mac-executor:
     macos:
-      xcode: "15.4.0"
-    resource_class: macos.m1.medium.gen1
+      xcode: "16.4.0"
+    resource_class: m4pro.medium
 
 jobs:
   prepare-build: