Split building and testing to improve parallelism

.github/workflows/build.yml

@@ -0,0 +1,21 @@
+on:
+  workflow_call:
+    inputs:
+      os:
+        required: true
+        type: string
+
+jobs:
+
+  tests:
+    strategy:
+      fail-fast: false
+    runs-on: ${{ inputs.os }}
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+        with:
+          flakehub: true
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - run: nix build

.github/workflows/ci.yml

@@ -14,23 +14,41 @@ permissions:
 
 jobs:
 
+  build_x86_64-linux:
+    uses: ./.github/workflows/build.yml
+    with:
+      os: UbuntuLatest32Cores128G
+
+  build_aarch64-linux:
+    uses: ./.github/workflows/build.yml
+    with:
+      os: UbuntuLatest32Cores128GArm
+
+  build_aarch64-darwin:
+    uses: ./.github/workflows/build.yml
+    with:
+      os: macos-latest
+
   test_x86_64-linux:
     uses: ./.github/workflows/test.yml
+    needs: build_x86_64-linux
     with:
       os: UbuntuLatest32Cores128G
 
   test_aarch64-linux:
     uses: ./.github/workflows/test.yml
+    needs: build_aarch64-linux
     with:
       os: UbuntuLatest32Cores128GArm
 
   test_aarch64-darwin:
     uses: ./.github/workflows/test.yml
+    needs: build_aarch64-darwin
     with:
       os: macos-latest
 
   vm_tests:
-    needs: test_x86_64-linux
+    needs: build_x86_64-linux
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -41,7 +59,7 @@ jobs:
       - run: nix build -L .#hydraJobs.tests.githubFlakes .#hydraJobs.tests.tarballFlakes
 
   flake_regressions:
-    needs: test_x86_64-linux
+    needs: build_x86_64-linux
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout nix