Refactor container build and installation pipeline to use configurable Makefile parameters (e.g. DISTROS, base images) and propagate them through all build, install, and test scripts

scripts/test/test-unit.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+echo "============================================================"
+echo ">>> Running UNIT tests in Arch container"
+echo "============================================================"
+
+docker run --rm \
+  -v "$(pwd):/src" \
+  -v "pkgmgr_nix_cache:/root/.cache/nix" \
+  --workdir /src \
+  -e PKGMGR_DEV=1 \
+  --entrypoint bash \
+  "package-manager-test-arch" \
+  -c '
+    set -e;
+    git config --global --add safe.directory /src || true;
+    nix develop .#default --no-write-lock-file -c \
+      python -m unittest discover \
+        -s tests/unit \
+        -t /src \
+        -p "test_*.py";
+  '