chore: Issue warning announcing entity's value_type as mandatory (#4833)

* feat: Make entity value_type mandatory with deprecation warning

- Add deprecation warning when value_type is not specified for an entity
- Add test cases to verify deprecation warning behavior
- Prepare for making value_type mandatory in next release

Issue: #4670

Co-Authored-By: Francisco Javier Arceo <[email protected]>
Signed-off-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* style: Fix import sorting in entity files

- Reorder imports according to PEP8
- Group standard library imports together
- Fix ruff linting issues

Co-Authored-By: Francisco Javier Arceo <[email protected]>
Signed-off-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Signed-off-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

sdk/python/feast/entity.py

@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import warnings
 from datetime import datetime
 from typing import Dict, List, Optional
 
@@ -79,6 +80,13 @@ def __init__(
             ValueError: Parameters are specified incorrectly.
         """
         self.name = name
+        if value_type is None:
+            warnings.warn(
+                "Entity value_type will be mandatory in the next release. "
+                "Please specify a value_type for entity '%s'." % name,
+                DeprecationWarning,
+                stacklevel=2,
+            )
         self.value_type = value_type or ValueType.UNKNOWN
 
         if join_keys and len(join_keys) > 1:

sdk/python/tests/unit/test_entity.py

@@ -11,6 +11,8 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import warnings
+
 import assertpy
 import pytest
 
@@ -73,3 +75,16 @@ def test_hash():
 
     s4 = {entity1, entity2, entity3, entity4}
     assert len(s4) == 3
+
+
+def test_entity_without_value_type_warns():
+    with pytest.warns(DeprecationWarning, match="Entity value_type will be mandatory"):
+        entity = Entity(name="my-entity")
+    assert entity.value_type == ValueType.UNKNOWN
+
+
+def test_entity_with_value_type_no_warning():
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
+        entity = Entity(name="my-entity", value_type=ValueType.STRING)
+    assert entity.value_type == ValueType.STRING