Github actions (CI) (#4)

A new github workflow added at `.github/workflows/ci.yaml` with three jobs:
- `build-cargo`: Sets up Rust toolchain (stable), checks out the current repository, places `reilabs/noir` at the appropriate folder, and finally runs `cargo build --release`.
- `test-cargo`: Depends on `build-cargo`. Runs the same steps, except the final step is replaced by a `cargo test` run.
- `build-lake`: Sets up Lean4 toolchain, checks out the current repository sparsely (i.e., only the `Lake` folder is fetched) and runs `lake build`.

The workflow runs on `push` and `pull-request` events.

.github/workflows/ci.yaml

@@ -0,0 +1,65 @@
+name: CI
+on: [push, pull_request]
+jobs:
+    build-lake:
+        runs-on: ubuntu-latest
+        steps:
+            - name: Checkout current branch (sparse)
+              uses: actions/checkout@v4
+              with:
+                sparse-checkout: |
+                  Lampe
+            - name: Set up Lean 4
+              uses: leanprover/lean-action@v1
+              with:
+                auto-config: false
+                build: false
+                test: false
+                lint: false
+                use-mathlib-cache: true
+                lake-package-directory: Lampe
+            - name: Build (lake)
+              working-directory: Lampe
+              run: lake build
+    build-cargo:
+      runs-on: ubuntu-latest
+      steps:
+          - name: Checkout current branch
+            uses: actions/checkout@v4
+            with:
+              path: lampe
+          - name: "Checkout reilabs/noir (branch: lampe)"
+            uses: actions/checkout@v4
+            with:
+              path: noir
+              ref: lampe
+              repository: reilabs/noir
+          - name: Set up Rust
+            uses: actions-rs/toolchain@v1
+            with:
+              toolchain: stable
+          - name: Build (cargo)
+            working-directory: lampe
+            run: cargo build --release
+    test-cargo:
+      needs: build-cargo
+      runs-on: ubuntu-latest
+      steps:
+        - name: Checkout current branch
+          uses: actions/checkout@v4
+          with:
+            path: lampe
+        - name: "Checkout reilabs/noir (branch: lampe)"
+          uses: actions/checkout@v4
+          with:
+            path: noir
+            ref: lampe
+            repository: reilabs/noir
+        - name: Set up Rust
+          uses: actions-rs/toolchain@v1
+          with:
+            toolchain: stable
+        - name: Test (cargo)
+          working-directory: lampe
+          run: cargo test
+