Fix justifications unpacking/repacking logic to handle finalized slot boundaries in state transition

[noopur23]

the justifications pruning in state in spec, so while packing in the state, the justifications and justification slots start from finalized slot + 1,

so this info needs to be used to unpack justifications from the parent state using parent's finalized, and needs to be repacked into the post state that is being constructed in the STF using the post state's finalized (updated if new finalization)