Add ngx_http_ipng_stats_module: per-VIP, per-device traffic counters

Full implementation of the nginx dynamic module with:
- SO_BINDTODEVICE-based per-interface traffic attribution
- Per-worker lock-free counters flushed to shared memory
- Prometheus text and JSON scrape endpoint at configurable location
- UDP-only global logtail (ipng_stats_logtail) for fire-and-forget
  access log streaming
- $ipng_source_tag nginx variable for use in log_format/map
- Histogram buckets, EWMA rate gauges, zone meta-metrics
- Debian packaging (libnginx-mod-http-ipng-stats)
- Robot Framework end-to-end tests via containerlab
- SPDX Apache-2.0 headers on all source files

tests/rf-run.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+# SPDX-License-Identifier: Apache-2.0
+# Test runner for nginx-ipng-stats-plugin robot tests.
+# Usage: ./rf-run.sh <runtime> <test_path>
+#   runtime: docker (default)
+#   test_path: path to .robot file or directory (default: all tests)
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+CLAB_BIN="${CLAB_BIN:-containerlab}"
+RUNTIME="${1:-docker}"
+TEST="${2:-${SCRIPT_DIR}}"
+
+mkdir -p "${SCRIPT_DIR}/out"
+
+# Create venv if needed
+if [ ! -d "${SCRIPT_DIR}/.venv" ]; then
+    python3 -m venv "${SCRIPT_DIR}/.venv"
+    "${SCRIPT_DIR}/.venv/bin/pip" install -q -r "${SCRIPT_DIR}/requirements.txt"
+fi
+
+source "${SCRIPT_DIR}/.venv/bin/activate"
+
+get_logname() {
+    local name
+    name="$(basename "$1" .robot)"
+    if [ -d "$1" ]; then
+        name="$(basename "$1")"
+    fi
+    echo "$name"
+}
+
+robot --consolecolors on -r none \
+    --variable CLAB_BIN:"${CLAB_BIN}" \
+    --variable runtime:"${RUNTIME}" \
+    -l "${SCRIPT_DIR}/out/$(get_logname "${TEST}")-${RUNTIME}-log" \
+    --output "${SCRIPT_DIR}/out/$(get_logname "${TEST}")-${RUNTIME}-out.xml" \
+    "${TEST}"