feat: add initial codspeed integration

Author: Tinche

.github/workflows/codspeed.yml

@@ -0,0 +1,42 @@
+name: CodSpeed Benchmarks
+
+on:
+  push:
+    branches: [main]
+    tags: ["*"]
+    paths:
+      - src/**.py
+      - bench/**
+      - .github/workflows/codspeed.yml
+  pull_request:
+    paths:
+      - src/**.py
+      - bench/**
+      - .github/workflows/codspeed.yml
+  workflow_dispatch:
+
+permissions:
+  contents: read # required for actions/checkout
+  id-token: write # required for OIDC authentication with CodSpeed
+  
+jobs:
+  codspeed:
+    name: Run CodSpeed benchmarks
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v6.0.0 # Use a fixed version
+        with:
+           persist-credentials: false
+      - uses: actions/setup-python@v6.1.0 # Use a fixed version
+        with:
+          python-version: "3.11" # Assuming Python 3.11, adjust if needed
+      - uses: hynek/setup-cached-uv@v2.3.0 # Use a fixed version
+
+      - name: Run CodSpeed benchmarks
+        uses: CodSpeedHQ/action@v4.4.1 # Use a fixed version
+        with:
+          mode: instrumentation
+          run: |
+            uv pip install pytest-codspeed
+            uv run pytest --codspeed bench/