add typehints to some code

[RayBB]

Problem

Sometimes I think I open a PR like #9116 and it gets lost because it doesn't have an issue. As such, I'm creating this issue.

I was digging around in the code for some reason or other and hit an area missing a lot of typehints so I added them where I could. I only added them in places where I was quite certain based on how they the values were being used.

Context

I now see this is related to #8028

Notes from this Issue's Lead

Proposal & constraints

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