Initiative: Integrate Flat storage with State sync

[Longarithm]

Core team Q2'2023 initiative.

Part of #8545. We plan to use flat storage to construct state parts instead of reading nodes from these parts from disk.

Tasks

• Construct state sync parts using flat storage #8898
• feat: create NodeStorage from checkpoint #8876
• Implement state parts in new format #8984
• Review feat(state-sync): DB Snapshots #9090 to be able to use renewed state sync dumping on live nodes

[Longarithm]

Implemented PoC for integration which works: #8927.
Added other issue requiring special attention: #8984.

[Longarithm]

While working, I came across several challenges related to Trie logic and testing. I managed to fix some of them to keep the project moving, and documented all known issues here: #8997.

[Longarithm]

The core team involvement mostly finishes here, as #8898 is merged. We'll still keep an eye on productionization, e.g. #9090 which aims to use snapshots as source of FlatState.
Node team expects that we can include this work in 1.36 :)

[Longarithm]

With #9090 we'll be able to use new state sync dumping on live nodes. It gives us option to snapshot flat storage and use it to construct state parts while real flat storage is keeping in sync.