feat(core): add scenario scope to surfnet_exportSnapshot RPC

[MicaiahReid]

• change registerScenario to proactively evaluate account overrides for scenario
• add new scope to exportSnapshot rpc to allow exporting a scenario

[lgalabru]

I'm confused, do we still need this PR @MicaiahReid ?

[MicaiahReid]

I'm confused, do we still need this PR @MicaiahReid ?

Hmm, good question.

This PR does a few potentially helpful things, if scenarios are to be more developed:

• proactively compiles all account changes for a scenario rather than lazily
  • so, when you register the scenario, it fetches all accounts, and generates the new account states and stores that
  • when you step through slots it's just applying the already computed account state, rather than fetching accounts and computing on the fly
• allows exporting those scenario account states as a snapshot, to be imported for tests

If we see scenarios being fleshed out further as a feature, this PR should probably be taken over the finish line. If not, we can probably close.