refactor: create workspace, move 'pacman' into pacman/ subfolder as workspace member

.github/workflows/tests.yaml

@@ -33,7 +33,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: target/vcpkg
-          key: A-vcpkg-${{ runner.os }}-${{ hashFiles('Cargo.toml', 'Cargo.lock') }}
+          key: A-vcpkg-${{ runner.os }}-${{ hashFiles('pacman/Cargo.toml', 'pacman/Cargo.lock') }}
           restore-keys: |
             A-vcpkg-${{ runner.os }}-
 
@@ -46,8 +46,10 @@ jobs:
         run: |
           cargo install cargo-vcpkg
           cargo vcpkg -v build
+        working-directory: pacman
 
       - uses: taiki-e/install-action@nextest
 
       - name: Run nextest
         run: cargo nextest run --workspace
+        working-directory: pacman