fix: make benches work again

Somehow in the past while splitting into many crates, we broke the bench
setup. This commit both fixes it, and adds a CI job that ensures it is
still working to avoid such silent failure in the future. The benchmarks
are not actually run, they would take forever on the slow GitHub Actions
runners, but they are at least compiled.

.github/workflows/qc.yaml

@@ -33,6 +33,26 @@ jobs:
       - name: Run Rust Formatting Script
         run: bash format_rust_code.sh --mode check
 
+  cargo-bench:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/cache@v3
+        with:
+          path: |
+            ~/.cargo/bin/
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+            target/
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+      - name: Install libsodium
+        run: sudo apt-get install -y libsodium-dev
+        # liboqs requires quite a lot of stack memory, thus we adjust
+        # the default stack size picked for new threads (which is used
+        # by `cargo test`) to be _big enough_. Setting it to 8 MiB
+      - run: RUST_MIN_STACK=8388608 cargo bench --no-run --workspace
+
   cargo-audit:
     runs-on: ubuntu-latest
     steps: