ci: 优化 Cargo 构建缓存

- 共享 deb 与 Docker 的 Linux cross 编译缓存
- 为 Windows MSVC 构建添加独立缓存
- 固定 cross 版本以保证缓存一致性

.github/workflows/docker.yml

@@ -42,11 +42,19 @@ jobs:
 
       - uses: dtolnay/rust-toolchain@stable
 
+      - name: Cache Rust dependencies
+        uses: Swatinem/rust-cache@v2
+        with:
+          # Reuse dependency artifacts produced by the deb job and vice versa.
+          shared-key: linux-cross-release
+          key: ${{ hashFiles('Cross.toml', 'build/cross/Dockerfile.*') }}
+          cache-all-crates: true
+
       - name: Install build dependencies
         run: |
           sudo apt-get update
           sudo apt-get install -y unzip xz-utils
-          cargo install cross --locked
+          cargo install cross --version 0.2.5 --locked
 
       - name: Build frontend
         working-directory: web