Add GitHub Actions CI workflow and test badge

Python 3.10/3.12 matrix on ubuntu-latest. dev extras include cvxpy for the
stochastic optimiser tests. 121 tests in suite.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: burningcost

.github/workflows/tests.yml

@@ -0,0 +1,26 @@
+name: Tests
+
+on:
+  push:
+    branches: [master, main]
+  pull_request:
+    branches: [master, main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.12"]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+      - name: Run tests
+        run: pytest

README.md

@@ -1,4 +1,5 @@
 # rate-optimiser
+[![Tests](https://github.com/burning-cost/rate-optimiser/actions/workflows/tests.yml/badge.svg)](https://github.com/burning-cost/rate-optimiser/actions/workflows/tests.yml)
 
 ![Python](https://img.shields.io/badge/python-3.10%2B-blue) ![License: MIT](https://img.shields.io/badge/license-MIT-green) ![PyPI](https://img.shields.io/pypi/v/rate-optimiser)