Small typing issues

[Zaczero]

https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/blob/b01694579d80ed72621c564e17ec0e3c298b3d88/stac_fastapi/core/stac_fastapi/core/core.py#L737C1-L751C20

When trying to use the delete items method I got confused by its typing:

1. It accepts kwargs but it ignores it, despite the database supporting refresh arg.
2. It states Optional[stac_types.Item] but it never returns anything.

Given the context of #342, I believe there needs to be a project typing overhaul because it's somewhat misleading.

[jonhealy1]

PR with #342 ?