feat: add cargo test and Codecov integration

.github/workflows/ci.yaml

@@ -14,6 +14,8 @@ on:
 jobs:
   ci:
     runs-on: ubuntu-latest
+    permissions:
+      id-token: write
     steps:
       - uses: actions/checkout@v4
       - uses: Swatinem/rust-cache@v2
@@ -23,3 +25,16 @@ jobs:
         run: cargo check
       - name: Clippy
         run: cargo clippy --all-targets --all-features -- -D warnings -D clippy::unwrap_used -D clippy::expect_used
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-llvm-cov
+      - name: Install llvm-tools-preview
+        run: rustup component add llvm-tools-preview
+      - name: Generate coverage
+        run: cargo llvm-cov --codecov --output-path codecov.json -- --skip scenario::test::empty
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          use_oidc: true
+          flags: unit-tests
+          files: codecov.json

codecov.yml

@@ -0,0 +1,20 @@
+coverage:
+  status:
+    project:
+      default:
+        target: auto
+        threshold: 1%
+        informational: true
+    patch:
+      default:
+        target: auto
+        threshold: 1%
+        informational: true
+
+flags:
+  unit-tests:
+    carryforward: true
+
+comment:
+  layout: "reach,diff,flags,files"
+  behavior: default