Use EnableNextSlotStateCache few more places

[terencechain]

What type of PR is this?

Feature

What does this PR do? Why is it needed?
Use #8357 in a few more places. Gated by the feature flag --enable-next-slot-state-cache
Which issues(s) does this PR fix?
N/A
Other notes for review
N/A

[nisdas]

Is it possible to do a bit of refactoring here and make all this logic under ProcessSlots ? That way we dont have to use this if else pattern everywhere and instead can just use it in one place. Also makes our code cleaner

[terencechain]

Is it possible to do a bit of refactoring here and make all this logic under ProcessSlots ? That way we dont have to use this if else pattern everywhere and instead can just use it in one place. Also makes our code cleaner

I tried. It's actually not a clean refactor. Reasons:
1.) We'll have to add root to ProcessSlots's arguments. There's quite a few usages that don't have access to root and don't care about it
2.) In order to get root from the less relevant functions, we'll either need to read from db, or cache, or HTR something, I'm afraid of introducing further runtime bottlenecks or bugs.

I'm leaning towards leave it as it is