Add GitHub Actions CI (ruff, mypy, pytest)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: monperrus

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+      - run: pip install -e .[dev]
+      - run: ruff check .
+      - run: mypy .
+      - run: pytest --cov=llmism --cov-report=term-missing