refactor(firestore): align decode_dict and PipelineResult.data return types with _BSONType

- Annotate decode_dict with Union[dict, Vector, _BSONType].
- Update PipelineResult.data to return dict | Vector | _BSONType | None.
- Import _BSONType under TYPE_CHECKING in pipeline_result.py.

Towards #18402

Author: ohmayr

packages/google-cloud-firestore/google/cloud/firestore_v1/_helpers.py

@@ -431,7 +431,7 @@ def _decode_bson_dict_recursive(data: Any) -> Any:
 def decode_dict(
     value_fields,
     client=None,
-) -> Union[dict, Vector, _BSONType, bytes]:
+) -> Union[dict, Vector, _BSONType]:
     """Converts a protobuf map of Firestore ``Value``-s.
 
     Args:
@@ -442,7 +442,7 @@ def decode_dict(
 
     Returns:
         Union[dict, ~google.cloud.firestore_v1.vector.Vector, \
-            ~google.cloud.firestore_v1.bson._BSONType, bytes]: A dictionary of native \
+            ~google.cloud.firestore_v1.bson._BSONType]: A dictionary of native \
         Python values, Vector, or BSON object converted from ``value_fields``.
     """
     value_fields_pb = getattr(value_fields, "_pb", value_fields)

packages/google-cloud-firestore/google/cloud/firestore_v1/pipeline_result.py

@@ -44,6 +44,7 @@
     from google.cloud.firestore_v1.async_transaction import AsyncTransaction
     from google.cloud.firestore_v1.base_client import BaseClient
     from google.cloud.firestore_v1.base_document import BaseDocumentReference
+    from google.cloud.firestore_v1.bson import _BSONType
     from google.cloud.firestore_v1.client import Client
     from google.cloud.firestore_v1.pipeline import Pipeline
     from google.cloud.firestore_v1.pipeline_expressions import Constant
@@ -138,7 +139,7 @@ def __eq__(self, other: object) -> bool:
             return NotImplemented
         return (self._ref == other._ref) and (self._fields_pb == other._fields_pb)
 
-    def data(self) -> dict | "Vector" | None:
+    def data(self) -> dict | "Vector" | "_BSONType" | None:
         """
         Retrieves all fields in the result.