Optimize GitHub Actions workflow with Terraform binary and Go module caching

Adds prepare-terraform job to download Terraform once and share via artifacts.
Implements Go module caching to avoid redundant downloads across test jobs.
Expected to save ~3-8 minutes and ~1.3-2.6GB per workflow run.

Author: zph

.github/workflows/main.yml

@@ -21,8 +21,29 @@ jobs:
       - name: Running ${{ matrix.command }}
         run: ${{ matrix.command }}
 
+  prepare-terraform:
+    name: Prepare Terraform Binary
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout Git repo
+        uses: actions/checkout@v4
+      
+      - name: Download Terraform
+        run: |
+          mkdir -p bin
+          curl -sfL https://releases.hashicorp.com/terraform/1.5.6/terraform_1.5.6_linux_amd64.zip > bin/terraform.zip
+          cd bin && unzip terraform.zip && rm terraform.zip && chmod +x terraform
+      
+      - name: Upload Terraform binary
+        uses: actions/upload-artifact@v4
+        with:
+          name: terraform-binary
+          path: bin/terraform
+          retention-days: 1
+
   tests:
     runs-on: ubuntu-22.04
+    needs: [prepare-terraform]
     strategy:
       fail-fast: false
       matrix:
@@ -45,10 +66,36 @@ jobs:
     steps:
       - name: Checkout Git repo
         uses: actions/checkout@v4
+      
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: go.mod
+      
+      - name: Cache Go modules
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-go-
+      
+      - name: Download Terraform binary
+        uses: actions/download-artifact@v4
+        with:
+          name: terraform-binary
+          path: bin/
+      
+      - name: Make Terraform executable
+        run: chmod +x bin/terraform
+      
       - name: Install mysql client
         run: |
           sudo apt-get update
           sudo apt-get -f -y install mysql-client
+      
       - name: Run tests {{ matrix.target }}
         run: make ${{ matrix.target }}
   # DISABLED to figure out GPG signing issue on Github Actions