fix: Preserve Pydantic validation in Config.__setattr__

Changed from object.__setattr__() to super().__setattr__() so that
Pydantic's validate_assignment=True works correctly. This fixes:
- test_loglevel_validation - now correctly rejects invalid loglevels
- test_fetch_format_validation - now correctly rejects invalid formats
- test_cache_path_string - now correctly coerces strings to Path

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/settings.py

@@ -957,7 +957,8 @@ def __setattr__(self, name: str, value: Any) -> None:
         except AttributeError:
             pass  # thread_safe not set yet (during __init__)
 
-        return object.__setattr__(self, name, value)
+        # Use super().__setattr__ to preserve Pydantic validation
+        return super().__setattr__(name, value)
 
     # Dict-like access for convenience
     def __getitem__(self, key: str) -> Any: