ci: cache CUDA compilation for Windows and Docker builds

scripts/ci-cuda-cache.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+mode="${1:-}"
+if [[ "$mode" != restore && "$mode" != save ]]; then
+    echo "Usage: $0 restore|save" >&2
+    exit 1
+fi
+
+cache_dir="${RUNNER_TEMP:?}/cuda-ccache"
+builder="${CUDA_CACHE_BUILDER:?}"
+work_dir="$(mktemp -d "${RUNNER_TEMP}/cuda-cache.XXXXXX")"
+trap 'rm -rf -- "$work_dir"' EXIT
+mkdir -p "$cache_dir"
+
+# Cache mounts are outside image layers; always execute the transfer RUN.
+if [[ "$mode" == restore ]]; then
+    cat > "$work_dir/Dockerfile" <<'DOCKERFILE'
+FROM ubuntu:24.04
+RUN --mount=type=cache,target=/root/.cache/ccache \
+    --mount=type=bind,source=.,target=/cache-input \
+    cp -a /cache-input/. /root/.cache/ccache/
+DOCKERFILE
+    docker buildx build --builder "$builder" --no-cache \
+        --file "$work_dir/Dockerfile" --output type=cacheonly "$cache_dir"
+else
+    cat > "$work_dir/Dockerfile" <<'DOCKERFILE'
+FROM ubuntu:24.04 AS transfer
+RUN --mount=type=cache,target=/root/.cache/ccache \
+    mkdir /cache-output && cp -a /root/.cache/ccache/. /cache-output/
+FROM scratch
+COPY --from=transfer /cache-output/ /
+DOCKERFILE
+    docker buildx build --builder "$builder" --no-cache \
+        --file "$work_dir/Dockerfile" \
+        --output "type=local,dest=$work_dir/export" "$work_dir"
+    # Replace only after export succeeds, including removal of evicted entries.
+    mv "$cache_dir" "$work_dir/previous-cache"
+    mv "$work_dir/export" "$cache_dir"
+fi