Update CircleCI to use Xcode 14.3.1 with m4pro.medium resource class

Fix CircleCI build failure caused by incompatible Xcode/resource class
combination. The previous configuration used Xcode 14.0.0 which is not
compatible with the new default m4pro.medium resource class.

Changes:
- Update Xcode from 14.0.0 to 14.3.1 (latest Xcode 14.x version)
- Explicitly specify resource_class: m4pro.medium
- This combination is supported per CircleCI's compatibility matrix

Xcode 14.0.0 only supports older M1/M2 resource classes which are being
deprecated in February 2026. Xcode 14.3.1 is compatible with the newer
M4 Pro resource classes and will be supported long-term.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>
Signed-off-by: David Scott <[email protected]>

Author: djs55

.circleci/config.yml

@@ -2,7 +2,8 @@ version: 2
 jobs:
   build:
     macos:
-      xcode: "14.0.0"
+      xcode: "14.3.1"
+    resource_class: m4pro.medium
     environment:
       OPAMYES: "1"
       OPAMJOBS: "2"