Fix coverage CI job by building project before running tests

The coverage job was failing because integration tests require the built wassette binary to be present in target/debug/wassette, but coverage was running tests without building first. This fix adds a build step before coverage generation to ensure the binary is available for integration tests.

Co-authored-by: Mossaka <[email protected]>

Author: Copilot

.github/workflows/rust.yml

@@ -131,6 +131,8 @@ jobs:
       uses: taiki-e/install-action@331a600f1b10a3fed8dc56f925012bede91ae51f # v2.47.11
       with:
         tool: cargo-llvm-cov
+    - name: Build project before coverage
+      run: just build
     - name: Generate code coverage
       run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info --ignore-run-fail
     - name: Upload coverage reports to Codecov