Persist Zig build caches in CI

.gitea/workflows/build-and-release.yml

@@ -23,6 +23,7 @@ jobs:
     name: Build executables
     runs-on: ubuntu-latest
     env:
+      ZIG_INSTALL_ROOT: /ci-cache/zig-chess/0.16.0/linux-amd64/tool
       ZIG_LOCAL_CACHE_DIR: /ci-cache/zig-chess/0.16.0/linux-amd64/local
       ZIG_GLOBAL_CACHE_DIR: /ci-cache/zig-chess/0.16.0/linux-amd64/global
 
@@ -30,10 +31,31 @@ jobs:
       - name: Checkout
         uses: https://github.com/actions/checkout@v4
 
-      - name: Set up Zig
-        uses: https://github.com/mlugg/setup-zig@v2
-        with:
-          version: 0.16.0
+      - name: Install pinned Zig from the persistent cache
+        run: |
+          set -eu
+          cache_parent="$(dirname "$ZIG_INSTALL_ROOT")"
+          mkdir -p "$cache_parent"
+          exec 9>"$cache_parent/.install.lock"
+          flock -x 9
+          if ! test -x "$ZIG_INSTALL_ROOT/zig" || \
+             ! test "$("$ZIG_INSTALL_ROOT/zig" version)" = "0.16.0"; then
+            archive="$(mktemp /tmp/zig-0.16.0.XXXXXXXX.tar.xz)"
+            staging="$(mktemp -d "$cache_parent/.tool.XXXXXXXX")"
+            trap 'rm -f "$archive"; rm -rf "$staging"' EXIT
+            curl --fail --location --retry 3 --retry-all-errors \
+              --output "$archive" \
+              https://ziglang.org/download/0.16.0/zig-x86_64-linux-0.16.0.tar.xz
+            printf '%s  %s\n' \
+              70e49664a74374b48b51e6f3fdfbf437f6395d42509050588bd49abe52ba3d00 \
+              "$archive" | sha256sum --check -
+            tar -xJf "$archive" --strip-components=1 -C "$staging"
+            rm -rf "$ZIG_INSTALL_ROOT"
+            mv "$staging" "$ZIG_INSTALL_ROOT"
+            rm -f "$archive"
+            trap - EXIT
+          fi
+          echo "$ZIG_INSTALL_ROOT" >> "$GITHUB_PATH"
 
       - name: Install shader compiler
         run: |