macos: enable Metal shader logging

This enables the compile options and Xcode configuration so that logging
in Metal shaders shows up in our Xcode debug console. This doesn't add
any log messages, but makes it so that when we iterate on the shaders in
the future, we can add and see logs to help us out.

.github/workflows/test.yml

@@ -196,6 +196,9 @@ jobs:
           name: ghostty
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
 
+      - name: XCode Select
+        run: sudo xcode-select -s /Applications/Xcode_16.0.app
+
       - name: Test All
         run: |
           # OpenGL
@@ -352,6 +355,9 @@ jobs:
           name: ghostty
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
 
+      - name: XCode Select
+        run: sudo xcode-select -s /Applications/Xcode_16.0.app
+
       - name: test
         run: nix develop -c zig build test