Add GitHub workflow for building the examples

.github/workflows/examples.yml

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+name: Build Examples
+
+on:
+  push:
+    branches: [ "main", "zig-*" ]
+    tags: [ 'v*.*.*' ]
+    
+  pull_request:
+    branches: [ "main", "zig-*" ]
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}_examples
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+      # This is used to complete the identity challenge
+      # with sigstore/fulcio when running outside of PRs.
+      id-token: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      # Set up BuildKit Docker container builder to be able to build
+      # multi-platform images and export cache
+      # https://github.com/docker/setup-buildx-action
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3 # v3.0.0
+
+      # Extract metadata (tags, labels) for Docker
+      # https://github.com/docker/metadata-action
+      - name: Extract Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5 # v5.0.0
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      # Build and push Docker image with Buildx (don't push on PR)
+      # https://github.com/docker/build-push-action
+      - name: Build and push Docker image
+        id: build-and-push
+        uses: docker/build-push-action@v5 # v5.0.0
+        with:
+          context: .
+          file: examples.Dockerfile
+          push: false
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}

build_all_examples.sh

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+#!/bin/bash
+
+set -e
+
+for x in ./examples/*/build.zig; do
+  EXAMPLEDIR=$(dirname "$x")
+
+  echo "Building example: $EXAMPLEDIR ..."
+
+  pushd $EXAMPLEDIR > /dev/null
+
+  zig build
+
+  popd > /dev/null
+done

build_all_examples_docker.sh

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+#!/bin/sh
+
+set -e
+
+IMAGE=zzmq_examples_347563478
+
+DOCKER_BUILDKIT=1 docker build . -t $IMAGE -f examples.Dockerfile

examples.Dockerfile

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+FROM alpine:3.19 as builder
+
+# install Zig 0.12 from Alpine edge community repo: https://pkgs.alpinelinux.org/package/edge/community/x86_64/zig
+RUN echo "@edge-community https://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories
+RUN apk add --no-cache zig@edge-community~=0.12.0
+
+# install dependencies
+RUN apk add --no-cache zeromq-dev clang bash
+
+COPY . /build/
+
+WORKDIR /build
+
+RUN ./build_all_examples.sh
+
+RUN touch /var/touched # dummy build output
+
+# empty result image
+FROM scratch
+
+COPY --from=builder /var/touched /tmp/touched