Add CI workflow for performance benchmarks

.github/workflows/benchmarks.yml

@@ -0,0 +1,77 @@
+name: Performance benchmarks
+
+on:
+  pull_request_target:
+    types: [opened, ready_for_review]
+    branches:
+      - main
+  issue_comment:
+    types: [created]
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  run-benchmarks:
+    if: >
+      github.event_name == 'pull_request_target' ||
+      (github.event_name == 'issue_comment' && contains(github.event.comment.body, '/rerun-benchmarks'))
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout PR branch
+        uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Add project directory to PYTHONPATH
+        run: echo "PYTHONPATH=$PYTHONPATH:$(pwd)" >> $GITHUB_ENV
+      - name: Install dependencies
+        run: pip install numpy pandas tqdm tabulate
+      - name: Checkout main branch
+        uses: actions/checkout@v4
+        with:
+          ref: main
+          repository: EwoutH/mesa
+      - name: Run benchmarks on main branch
+        working-directory: benchmarks
+        run: python global_benchmark.py
+      - name: Upload benchmark results
+        uses: actions/upload-artifact@v4
+        with:
+          name: timings-main
+          path: benchmarks/timings_1.pickle
+      - name: Checkout PR branch
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
+          fetch-depth: 0
+          persist-credentials: false
+          clean: false
+      - name: Download benchmark results
+        uses: actions/download-artifact@v4
+        with:
+          name: timings-main
+          path: benchmarks
+      - name: Run benchmarks on PR branch
+        working-directory: benchmarks
+        run: python global_benchmark.py
+      - name: Run compare timings and encode output
+        working-directory: benchmarks
+        run: |
+          TIMING_COMPARISON=$(python compare_timings.py | base64 -w 0)  # Base64 encode the output
+          echo "TIMING_COMPARISON=$TIMING_COMPARISON" >> $GITHUB_ENV
+      - name: Comment PR
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const output = Buffer.from(process.env.TIMING_COMPARISON, 'base64').toString('utf-8');
+            const issue_number = context.issue.number;
+            github.rest.issues.createComment({
+              issue_number: issue_number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: 'Performance benchmarks:\n\n' + output
+            });