fix: fetch(attrs, as_dict=True) no longer includes unrequested primary key

In 0.14.x, fetch('col1', 'col2', as_dict=True) returned dicts containing
only the requested attributes. In 2.x, proj() always includes primary key
attributes, so the returned dicts contained extra keys the caller didn't ask
for. Filter the dicts to only include requested attributes, restoring
backward compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/expression.py

@@ -716,7 +716,7 @@ def fetch(
         import warnings
 
         warnings.warn(
-            "fetch() is deprecated in DataJoint 2.0. " "Use to_dicts(), to_pandas(), to_arrays(), or keys() instead.",
+            "fetch() is deprecated in DataJoint 2.0. Use to_dicts(), to_pandas(), to_arrays(), or keys() instead.",
             DeprecationWarning,
             stacklevel=2,
         )
@@ -748,7 +748,10 @@ def is_key(attr):
                         proj_attrs.extend(self.primary_key)
                     else:
                         proj_attrs.append(attr)
-                return self.proj(*proj_attrs).to_dicts(order_by=order_by, limit=limit, offset=offset, squeeze=squeeze)
+                dicts = self.proj(*proj_attrs).to_dicts(order_by=order_by, limit=limit, offset=offset, squeeze=squeeze)
+                # Filter to only requested attributes (proj always includes primary key)
+                requested = set(proj_attrs)
+                return [{k: v for k, v in d.items() if k in requested} for d in dicts]
             else:
                 # fetch('col1', 'col2') or fetch('col1', 'col2', as_dict=False) -> tuple of arrays
                 # This matches DJ 1.x behavior where fetch('col') returns array(['alpha', 'beta'])