citizen: add foundry CI pipeline

.github/workflows/ci.yml

@@ -0,0 +1,49 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  FOUNDRY_PROFILE: ci
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+        with:
+          version: nightly
+
+      - name: Install dependencies
+        run: forge install
+
+      - name: Check formatting
+        run: forge fmt --check
+
+      - name: Build contracts
+        run: forge build --sizes
+
+      - name: Run tests
+        run: forge test -vvv
+
+      - name: Run snapshot (gas)
+        run: forge snapshot
+
+      - name: Check coverage
+        run: forge coverage
+
+  slither:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run Slither
+        uses: crytic/slither-action@v0.4.0
+        continue-on-error: true