feat: upgrade actions/cache to v4 and clean up imports in main.rs

.github/actions/setup-rust/action.yml

@@ -22,7 +22,7 @@ runs:
         fetch-depth: 0
 
     - name: Cache cargo registry
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.cargo/registry
         key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
@@ -30,7 +30,7 @@ runs:
           ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
 
     - name: Cache cargo index
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.cargo/index
         key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.lock') }}
@@ -51,7 +51,7 @@ runs:
           ${{ runner.os }}-rustup-
 
     - name: Cache cargo build (target)
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: target
         key: ${{ runner.os }}-cargo-build-${{ hashFiles('**/Cargo.lock') }}