Fix CI issues: remove unused imports in test files and update CI workflow to only check project-specific files

tests/conftest.py

@@ -1,6 +1,5 @@
 import pytest
 import tempfile
-import os
 from pathlib import Path
 
 
@@ -65,4 +64,4 @@ cmd cargo build --release
 - 1700000002
 cmd curl localhost:8080/api/health
     """.strip())
-    return history_file
+    return history_file