Type hint split query (#988)

* WIP typehinting

* WIP type hinting

* fix mypy errors

* add a few more typehints

* typing copilot tighten

* add line break to mypy.ini

* use Sequence instead of List

* use SelectionNode rather than FieldNode for some type hints

Co-authored-by: Selene Chew <[email protected]>

Author: chewselene