.github/workflows: Improve pipeline with some parallel steps

TODO

.github/workflows/.call-nix.yml

@@ -0,0 +1,30 @@
+name: Call Nix
+
+on:
+  workflow_call:
+    inputs:
+      cmd:
+        description: Command to invoke post-setup
+        required: true
+        type: string
+
+jobs:
+  setup:
+    name: ${{ inputs.cmd }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Free Disk Space
+        uses: jlumbroso/[email protected]
+
+      - name: Checkout Repository
+        uses: actions/[email protected]
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v30
+        with:
+          extra_nix_config: |
+            allow-import-from-derivation = false
+            eval-cache = false
+
+      - name: Invoke Command
+        run: ${{ inputs.cmd }}

.github/workflows/build.yml

@@ -7,28 +7,19 @@ on:
       - staging
 
 jobs:
-  tests:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/[email protected]
+  check:
+    name: Check Flake Outputs
+    uses: ./.github/workflows/.call-nix.yml
+    with:
+      cmd: nix flake check
 
-      - name: Free Disk Space
-        uses: jlumbroso/[email protected]
-        with:
-          tool-cache: true
-
-      - name: Install Nix
-        uses: cachix/install-nix-action@v30
-        with:
-          extra_nix_config: |
-            allow-import-from-derivation = false
-            eval-cache = false
-
-      - name: Run Flake Check
-        run: nix flake check
-
-      - name: Build NixOS Configurations
-        run: |
-          nix build '.#nixosConfigurations.LAPTOP-3DT4F02.config.system.build.toplevel'
-          nix build '.#nixosConfigurations.DESKTOP-3DT4F02.config.system.build.toplevel'
-          nix build '.#nixosConfigurations.ISO-3DT4F02.config.system.build.isoImage'
+  build:
+    name: Build Flake Outputs
+    strategy:
+      matrix:
+        outputs: ['nixosConfigurations.LAPTOP-3DT4F02.config.system.build.toplevel',
+                  'nixosConfigurations.DESKTOP-3DT4F02.config.system.build.toplevel',
+                  'nixosConfigurations.ISO-3DT4F02.config.system.build.isoImage']
+    uses: ./.github/workflows/.call-nix.yml
+    with:
+      cmd: nix build '.#${{ matrix.outputs }}'