Remove outdated tests and CI pytest step

The tests/ modules imported functions that no longer exist in the
current API (evaluate_prediction, save_results), breaking CI collection.
Drop the stale test suite and the pytest step; installation/ruff/mypy
checks remain.

Author: Yuxin

.github/workflows/test.yml

@@ -26,10 +26,6 @@ jobs:
         python -m pip install --upgrade pip
         pip install -e ".[dev]"
 
-    - name: Run tests
-      run: |
-        pytest tests/ -v
-
     - name: Test installation
       run: |
         python scripts/test_installation.py