Improve logic for retrieving runtime context for specific block.

[Zurcusa]

Currently we only store the runtime code in the DB during warp sync. We also store runtime instances in memory until a block is finalized. We need to improve 2 things:

• Only create runtime instances when runtime code changes. (this might require splitting the trie storage from the runtime since we want to have separate in memory execution changes for non finalized blocks)
• Make it possible to retrieve and create runtime instances for blocks in case they do not use the latest runtime code.