fix: restore Zig 0.16-dev APIs and use latest from pantry

Revert 0.15.1 API downgrade. CI now installs ziglang.org@latest
which resolves to the 0.16-dev build in the pantry registry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chrisbbreuer

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        zig-version: ['0.15.1']
+        zig-version: ['latest']
       fail-fast: false
     steps:
       - uses: actions/checkout@v4
@@ -30,5 +30,5 @@ jobs:
       - uses: actions/checkout@v4
       - uses: home-lang/pantry-setup@v1
         with:
-          packages: ziglang.org@0.15.1
+          packages: ziglang.org@latest
       - run: zig fmt --check .