feat: install juggler and eicrecon with spack

This makes more sense as part of the jug_dev step, since that's where large dependencies are installed with the full benefit of caching.

spack-environment/packages.yaml

@@ -112,6 +112,10 @@ packages:
     require:
     - '@12.1'
     - -debuginfod
+  g4ndl:
+    externals:
+    - spec: g4ndl@4.7
+      prefix: /opt/software/externals/g4ndl
   geant4:
     require:
     - '@11.1.2.east'