ci: pin Ruff for deterministic checks (#22)

Co-authored-by: Codex <noreply@openai.com>

Author: Pigbibi

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
         run: |
           set -euo pipefail
           python -m pip install --upgrade pip
-          python -m pip install -e '.[test]' ruff
+          python -m pip install -e '.[test]' 'ruff==0.15.22'
           python -m pip install --no-deps -e external/QuantPlatformKit -e external/CnEquityStrategies
 
       - name: Run ruff