add compose-based test runner for Python 2.7

Dockerfile.test builds production image with pytest baked in.
compose.test.yml mounts source as volume for fast iteration.
Usage: podman-compose -f compose.test.yml run --rm test

Dockerfile.test

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+FROM python:2.7-slim
+
+WORKDIR /app
+
+RUN sed -i 's/deb.debian.org/archive.debian.org/g' /etc/apt/sources.list && \
+    sed -i 's/security.debian.org/archive.debian.org/g' /etc/apt/sources.list && \
+    sed -i '/buster-updates/d' /etc/apt/sources.list && \
+    echo 'deb http://archive.debian.org/debian-security buster/updates main' >> /etc/apt/sources.list && \
+    apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install -y --no-install-recommends gcc libc-dev && \
+    rm -rf /var/lib/apt/lists/*
+
+RUN pip install --upgrade "pip<21" "setuptools<45" "wheel<0.38"
+
+COPY requirements.txt .
+RUN pip install -r requirements.txt || true
+RUN pip install pytest
+
+RUN mkdir -p /app/data && \
+    python -c "import pyasn" 2>/dev/null && \
+    pyasn_util_download.py --latest && \
+    pyasn_util_convert.py --single rib.*.bz2 /app/data/ipasn.dat && \
+    rm -f rib.*.bz2 || \
+    echo "pyasn database setup skipped"
+
+RUN apt-get purge -y gcc libc-dev && apt-get autoremove -y || true
+
+CMD ["python", "-m", "pytest", "tests/", "-v", "--tb=short"]

compose.test.yml

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+# PPF test runner (Python 2.7, production deps + pytest)
+#
+# Mounts source and tests as volumes so no rebuild needed between runs.
+#
+# Usage:
+#   podman-compose -f compose.test.yml run --rm test
+#   podman-compose -f compose.test.yml run --rm test python -m pytest tests/test_fetch.py -v
+
+services:
+  test:
+    container_name: ppf-test
+    build:
+      context: .
+      dockerfile: Dockerfile.test
+    volumes:
+      - .:/app:ro,Z
+    working_dir: /app
+    command: python -m pytest tests/ -v --tb=short