Add GitHub Actions workflow for CI

- Created .github/workflows/ci.yml to automate build and test on push and pull requests.
- Used actions/checkout@v6 and bazelbuild/setup-bazelisk@v3.

Author: cblichmann

.github/workflows/ci.yml

@@ -0,0 +1,24 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build_and_test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v6
+
+    - name: Set up Bazel
+      uses: bazelbuild/setup-bazelisk@v3
+
+    - name: Build and Test
+      run: |
+        export CC=clang
+        export CXX=clang++
+        bazelisk test //vxsig/...