Revisit historical TX handling

We've had some issues and long-lived bugs recently, for instance https://github.com/microsoft/CCF/pull/7755

Historical cache arch needs revisiting. Also, some dumping some related things.

- [ ] Messy receipt population logic, we should do smth about that
- [ ] Historical adapter populates endorsements AND COSE endorsements unconditionally, maybe it shouldn't? Maybe we should serve them on demand? COSE endorsements are quick because of prefetching done in #7518 , but regular ones are still fetched in the loop
- [ ] To top the previous off, regular endorsements are loaded one-per-poke on average, so needs poking 10x for pre-10-DR receipt? It's odd, and isn't good for SCITT scenarios maybe, which we maybe need to focus on.
- [ ] With regards to the endorsement, we may serve them separately via a dedicated endpoint? (mentioned in #6560)

Start by reading the historical cache and adapter discussion in PR #7755, then review the prefetching change in #7518 and the dedicated-endpoint discussion in #6560. Clarify the intended receipt and endorsement behavior, including SCITT needs, before identifying implementation files and tests. Done should mean an agreed scope and verified handling for receipt and endorsement retrieval.

Written by the indexing model from the issue text.