What this PR does / why we need it:

feast plan raises for a @batch_feature_view with a transformation as soon as anything in it differs from the registry. feast apply raises too: with the default local provider and SQLite online store it runs the same plan first. To reproduce, apply such a repo with tags={"team": "a"}, change the tag to "b" and run feast plan:

ValueError: Protocol message FeatureViewSpec has no "user_defined_function" field.

With this change feast plan prints the diff and feast apply goes through.

Cause: diff_registry_objects calls HasField("user_defined_function") on every spec whose feature_transformation changed. That deprecated field exists on OnDemandFeatureViewSpec and StreamFeatureViewSpec, not on FeatureViewSpec. A view read back from the registry never carries the declared transformation bytes, so any change to the view reaches this branch.

The fix reads the field only when the spec has it (hasattr, as on_demand_feature_view.py does). On demand views behave as before. Not covered here: a change to only the function body of a batch view is still not detected, because the view's __eq__ ignores the transformation.

Which issue(s) this PR fixes:

No issue, found while checking feast plan diffs.

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests

Added test_diff_batch_feature_view_with_transformation next to test_diff_odfv in sdk/python/tests/unit/diff/test_registry_diff.py. It diffs a view read back from its proto against a changed declaration: a tags change reports only tags, and a tags plus function text change reports tags and feature_transformation.body_text. It fails on master with the ValueError above and passes with the fix: pytest sdk/python/tests/unit/diff/test_registry_diff.py -k test_diff_batch_feature_view_with_transformation gives 1 passed, the whole file 6 passed. ruff check and ruff format --check are clean on both files.