ci: cache Go tools, bump action versions, use golangci-lint env var

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches: [master]
 
+env:
+  GOLANGCI_LINT_VERSION: v2.8.0
+
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -18,10 +21,16 @@ jobs:
         go-version: '1.26'
         cache: true
 
+    - name: Cache Go tools
+      uses: actions/cache@v5
+      with:
+        path: ~/go/bin
+        key: go-tools-${{ runner.os }}-goimports-latest-golangci-lint-${{ env.GOLANGCI_LINT_VERSION }}
+
     - name: Install tools
       run: |
-        go install golang.org/x/tools/cmd/goimports@latest
+        which goimports || go install golang.org/x/tools/cmd/goimports@latest
-        go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.8.0
+        which golangci-lint || go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@${{ env.GOLANGCI_LINT_VERSION }}
     
-    - name: Build
+    - name: Lint & Build
       run: make all