Add vcpkg download cache and retry steps to linux CI job

Co-authored-by: Valorith <76063792+Valorith@users.noreply.github.com>

.github/workflows/build.yaml

@@ -52,6 +52,33 @@ jobs:
       - name: Mark workspace safe
         run: git config --global --add safe.directory "$GITHUB_WORKSPACE"
 
+      - name: Cache vcpkg downloads
+        uses: actions/cache@v4
+        with:
+          path: submodules/vcpkg/downloads
+          key: ${{ runner.os }}-vcpkg-downloads-${{ hashFiles('submodules/vcpkg/vcpkg.json', 'submodules/vcpkg/ports/**', 'submodules/vcpkg/versions/**') }}
+          restore-keys: |
+            ${{ runner.os }}-vcpkg-downloads-
+
+      - name: vcpkg install (retry)
+        working-directory: ${{ github.workspace }}
+        run: |
+          set -e
+          cd submodules/vcpkg
+          ./bootstrap-vcpkg.sh -disableMetrics
+
+          for i in 1 2 3 4 5; do
+            echo "vcpkg install attempt $i..."
+            if ./vcpkg install --triplet x64-linux; then
+              exit 0
+            fi
+            echo "vcpkg install failed; sleeping before retry..."
+            sleep $((i * 10))
+          done
+
+          echo "vcpkg install failed after retries"
+          exit 1
+
       - name: Build
         working-directory: ${{ github.workspace }}
         run: |