Fix PaginationParams attributes types

The `page_size` and `page_token` attributes of the `PaginationParams`
class are not optional, so they should not be declared as `int | None`.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/client/common/pagination/__init__.py

@@ -19,10 +19,10 @@
 class Params:
     """Parameters for paginating list requests."""
 
-    page_size: int | None = None
+    page_size: int
     """The maximum number of results to be returned per request."""
 
-    page_token: str | None = None
+    page_token: str
     """The token identifying a specific page of the list results."""
 
     @classmethod