Add dependencies for building package cffi

This fails on armv6 and armv7 builds, probably because certain packages
no longer come prebuilt for those targets; we really need to build them
ourselves.

See also: https://cryptography.io/en/latest/installation/

.github/workflows/docker-publish.yml

@@ -69,7 +69,7 @@ jobs:
         uses: docker/build-push-action@0565240e2d4ab88bba5387d719585280857ece09 # v5.0.0
         with:
           context: .
-          platforms: linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v6
+          platforms: linux/amd64,linux/arm64,linux/arm/v7
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}

Dockerfile

@@ -1,7 +1,19 @@
 FROM python:3.12-slim
 WORKDIR /app
 COPY requirements.txt ./
-RUN pip install --no-cache-dir -r requirements.txt
+
+# The tmpfs mount is a workaround
+# https://github.com/rust-lang/cargo/issues/8719
+RUN --mount=type=tmpfs,target=/root/.cargo \
+    apt-get update \
+ && apt-get install --yes --no-install-recommends \
+        build-essential libssl-dev libffi-dev cargo pkg-config \
+ && pip install --no-cache-dir -r requirements.txt \
+ && apt-get autoremove --purge --yes \
+        build-essential libssl-dev libffi-dev cargo pkg-config \
+ && apt-get clean \
+ && rm -rf /root/.cache
+
 COPY . .
 ARG VERSION_TAG=unknown
 ENV MQTT4DSMR_VERSION=$VERSION_TAG