Use target checkpoint state to verify attestations

[twoeths]

Describe the bug

Right now we use the attested block root's state to verify attestations, we should use the the target checkpoint state to verify attestations instead.

Expected behavior

Already implemented in #4849 but due to the memory issue we mark it as a TODO until a 'proper' regen/cache strategy is implemented

[wemeetagain]

I think this is a duplicate of #4831

[twoeths]

duplicated to #4831