Harden TTL load paths #5020
Description
Currently, TTL and it's affiliated ContractData/ContractCode must be loaded separately. However, there should be no reason to load a data/code entry without it's associated TTL, so this interface can lead to footguns. We should refactor such that both the TTL and associated data/code entry are loaded at the same time and returned as some unified struct.
I believe @graydon is already working on hardening the data access layer with some compile time checks and type aliasing in #4971, so we should probably hold of on this until that is finished.