common: Persist binary packages between runs

lib/common.sh

@@ -6,9 +6,11 @@ buildah_run_script() {
     shift
     script=$(readlink -f "$1")
     shift
+    mkdir -p binpkgs
     buildah run \
         --mount type=cache,target=/var/db/repos/gentoo \
         --mount type=cache,target=/var/cache \
+        --mount type=bind,src="${PWD}"/binpkgs,target=/var/cache/binpkgs,rw,z \
         --mount type=bind,src="${script}",target=/run/script,ro,z \
         --tty=false \
         -e FEATURES='-ipc-sandbox -network-sandbox -pid-sandbox' \