chore: add depreciation warning for generation_number

Author: Pulkit0110

google/cloud/storage/asyncio/async_multi_range_downloader.py

@@ -208,6 +208,10 @@ def __init__(
                     "Cannot set both 'generation' and 'generation_number'. "
                     "Use 'generation' for new code."
                 )
+            logger.warning(
+                "'generation_number' is deprecated and will be removed in a future "
+                "major release. Please use 'generation' instead."
+            )
             generation = kwargs.pop("generation_number")
 
         raise_if_no_fast_crc32c()

tests/unit/asyncio/test_async_multi_range_downloader.py

@@ -407,7 +407,7 @@ async def close_side_effect():
     )
     @pytest.mark.asyncio
     async def test_create_mrd_with_generation_number(
-        self, mock_cls_async_read_object_stream
+        self, mock_cls_async_read_object_stream, caplog
     ):
         # Arrange
         mock_client = mock.MagicMock()
@@ -430,6 +430,10 @@ async def test_create_mrd_with_generation_number(
 
         # Assert
         assert mrd.generation == _TEST_GENERATION_NUMBER
+        assert len(caplog.records) == 1
+        record = caplog.records[0]
+        assert record.levelname == "WARNING"
+        assert "'generation_number' is deprecated" in record.message
 
     @pytest.mark.asyncio
     async def test_create_mrd_with_both_generation_and_generation_number(self):