fix: Make R bridge import optional in test_dataset_attribution

The unconditional import of RPythonBridge was causing CI failures
since the cross_validation module is only available locally.
Wrap the import in try/except like other test files.

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

Author: dshkol

tests/test_dataset_attribution.py

@@ -9,8 +9,14 @@
 sys.path.insert(0, str(Path(__file__).parent.parent))
 import pycancensus as pc
 
-# Import R bridge for cross-validation
-from tests.cross_validation.utils.r_python_bridge import RPythonBridge
+# Import R bridge for cross-validation (optional - only available locally)
+try:
+    from tests.cross_validation.utils.r_python_bridge import RPythonBridge
+
+    R_AVAILABLE = True
+except ImportError:
+    R_AVAILABLE = False
+    RPythonBridge = None
 
 
 class TestDatasetAttribution: