Allow configuring last state to be kept

[asdacap]

• Snap protocol requires that the last 128 state be available.
• This is also useful for eth_call RPC where user may want a certain window of state to be available.
• This create a new state layout agnostic config --State.KeepLastNState 64 so that this window can be configured.
  • No, I don't like the name too, give me a good one.

Changes

• Add config.
• Integrate with TrieStore.

Types of changes

What types of changes does your code introduce?

• New feature (a non-breaking change that adds functionality)

Testing

Requires testing

• Yes
• No

If yes, did you write tests?

• Yes
• No

Notes on testing

• Can snap serve from old state. (client hooked up to use pivot head-70 instead of head).
• Snap hive test (its running on archive, so has no effect).