Add CI test

Author: tkittel

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/test.yml

@@ -0,0 +1,34 @@
+name: test
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '8 15 * * 0'  # 8:15 every Monday
+
+jobs:
+  build_and_test_plugin:
+    strategy:
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+
+    name: ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+      with:
+        path: src
+
+    - name: Install dependencies
+      run: pip install 'ncrystal>=4.1.4'
+
+    - name: Install plugin
+      run: pip install ./src
+
+    - name: Verify plugin loading
+      run: ncrystal-pluginmanager --test CrysExtn
+
+    - name: Use explicit plugin file
+      run: nctool -d 'plugins::CrysExtn/Be_sg194_BC_pure_scndI.ncmat'