ci: add Spack install + smoke test workflow

.github/workflows/spack.yml

@@ -0,0 +1,56 @@
+name: Spack
+on:
+    push:
+    pull_request:
+    schedule:
+        - cron: '17 3 * * 0'
+
+concurrency:
+    group: ${{ github.workflow }}-${{ github.ref }}
+    cancel-in-progress: true
+
+jobs:
+    spack-install:
+        name: Spack install + smoke test
+        runs-on: ubuntu-latest
+        steps:
+          - uses: actions/checkout@v4
+
+          - name: Set up Spack with buildcache
+            uses: spack/setup-spack@v3
+            with:
+                # Pinned to a specific commit of sbryngelson/spack-packages
+                # until spack/spack-packages merges the mfc recipe.
+                # Update this SHA when the recipe branch advances.
+                packages_repository: sbryngelson/spack-packages
+                packages_ref: f0bb11a611fb7f311e788da778208be234601797
+                buildcache: true
+
+          - name: Cache Spack install store
+            uses: actions/cache@v4
+            with:
+                path: |
+                    spack/opt
+                    spack/var/spack/cache
+                key: spack-store-${{ runner.os }}-${{ hashFiles('spack-packages/repos/spack_repo/builtin/packages/mfc/package.py', 'spack-packages/repos/spack_repo/builtin/packages/cantera/package.py', 'spack-packages/repos/spack_repo/builtin/packages/py_pyrometheus/package.py') }}
+                restore-keys: spack-store-${{ runner.os }}-
+
+          - name: Install mfc (defaults to +mpi +pre_process +simulation +post_process)
+            run: spack install --reuse mfc
+
+          - name: Smoke test
+            run: |
+                source spack/share/spack/setup-env.sh
+                spack load mfc
+                prefix="$(spack location -i mfc)"
+                echo "MFC prefix: $prefix"
+                for t in pre_process simulation post_process; do
+                    test -x "$prefix/bin/$t" || { echo "missing binary: $t"; exit 1; }
+                    echo "found: $prefix/bin/$t"
+                done
+                test -x "$prefix/bin/mfc" || { echo "missing shim: mfc"; exit 1; }
+                echo "found shim: $prefix/bin/mfc"
+                cd "$prefix/share/mfc"
+                ./mfc.sh run --prebuilt-prefix="$prefix" \
+                             --mpi -N 1 -n 1 --dry-run \
+                             examples/1D_sodshocktube/case.py