feat: remove staging layer in container build

This PR removes the staging layer.

containers/jug/dev.Dockerfile

@@ -157,6 +157,7 @@ make --jobs ${jobs} --keep-going --directory /opt/spack-environment \
   SPACK_ENV=${SPACK_ENV} \
   BUILDCACHE_OCI_PROMPT="eicweb" \
   BUILDCACHE_OCI_FINAL="ghcr"
+spack gc --yes-to-all
 spack find --long --no-groups \
 | sed -e '1,/Installed packages/d;s/\([^@]*\).*/\1/g' \
 | uniq -D -f1 | grep -v -w -e "\(epic\|py-pip\|py-cython\)" \
@@ -208,6 +209,7 @@ spack concretize --fresh --force
 make --jobs ${jobs} --keep-going --directory /opt/spack-environment \
   SPACK_ENV=${SPACK_ENV} \
   BUILDCACHE_OCI_FINAL="eicweb"
+spack gc --yes-to-all
 spack find --long --no-groups \
 | sed -e '1,/Installed packages/d;s/\([^@]*\).*/\1/g' \
 | uniq -D -f1 | grep -v -w -e "\(epic\|py-pip\|py-cython\)" \
@@ -253,9 +255,6 @@ WORKDIR /
 ## ========================================================================================
 FROM builder as staging
 
-# Garbage collect in environment
-RUN spack -e ${SPACK_ENV} gc -y
-
 # Garbage collect in git
 #RUN git -C $SPACK_ROOT gc --prune=all --aggressive