use scale_factor and unit in cast_value for datetime

Author: d-v-b

src/zarr/core/dtype/npy/time.py

@@ -240,7 +240,7 @@ def from_json_value(self, data: JSON, *, zarr_format: ZarrFormat) -> np.datetime
         raise TypeError(f"Invalid type: {data}. Expected an integer.")  # pragma: no cover
 
     def _cast_value_unsafe(self, data: object) -> np.datetime64:
-        return self.to_dtype().type(data)  # type: ignore[no-any-return, call-overload]
+        return self.to_dtype().type(data, f"{self.scale_factor}{self.unit}")  # type: ignore[no-any-return, call-overload]
 
     @classmethod
     def check_json(cls, data: JSON, zarr_format: ZarrFormat) -> TypeGuard[JSON]: