ci(build-docs): Restore GHA-level caching

.github/workflows/build_deploy.yml

@@ -84,8 +84,18 @@ jobs:
         with:
           submodules: 'recursive'
           fetch-depth: 1
-
+      - name: Calculate cache key
+        id: cache-key
+        run: |
+          echo "cache-key=$(scripts/metacachekey metanorma src-documents/metanorma-${{ matrix.doc_type }}.yml)" >> $GITHUB_OUTPUT
+      - name: Restore cache
+        id: cache
+        uses: actions/cache@v4
+        with:
+          path: _site/${{ matrix.doc_type }}
+          key: ${{ steps.cache-key.outputs.cache-key }}
       - name: Metanorma generate site
+        if: steps.cache.outputs.cache-hit != 'true'
         uses: actions-mn/build-and-publish@main
         with:
           destination: artifact
@@ -94,6 +104,12 @@ jobs:
           artifact-name: metanorma-docs-${{ matrix.doc_type }}
           source-path: ./
           config-file: src-documents/metanorma-${{ matrix.doc_type }}.yml
+      - name: Save artifacts
+        if: steps.cache.outputs.cache-hit == 'true'
+        uses: actions/upload-artifact@v4
+        with:
+          name: metanorma-docs-${{ matrix.doc_type }}
+          path: _site/${{ matrix.doc_type }}
 
   #
   # At the very end, integrate them all with Jekyll.