ci: merge coverage workflow into CI

Both workflows had identical triggers, runner, and duplicate
checkout/toolchain/cache steps. Coverage now runs as the final
steps of the existing CI job.

Author: markovejnovic

.github/workflows/ci.yml

@@ -29,3 +29,14 @@ jobs:
         run: cargo test --workspace
       - name: Build example
         run: cargo test --manifest-path examples/quecto-repl/quecto-vm/Cargo.toml
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-tarpaulin
+      - name: Generate coverage
+        run: cargo tarpaulin --workspace --exclude hsrs-macros --out xml --output-dir coverage
+      - name: Upload to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          files: coverage/cobertura.xml
+          fail_ci_if_error: false
+          token: ${{ secrets.CODECOV_TOKEN }}