Integrate memory overlay in canonical state

[mattsse]

in addition to tracking the the executed block, we also need to be able to serve the state at a canonical block, which works like:

reth/crates/engine/tree/src/tree/mod.rs

Lines 575 to 589 in 8c8702b

	/// Return state provider with reference to in-memory blocks that overlay database state.
	fn state_provider(
	&self,
	hash: B256,
	) -> ProviderResult<MemoryOverlayStateProvider<Box<dyn StateProvider>>> {
	let mut in_memory = Vec::new();
	let mut parent_hash = hash;
	while let Some(executed) = self.state.tree_state.blocks_by_hash.get(&parent_hash) {
	parent_hash = executed.block.parent_hash;
	in_memory.insert(0, executed.clone());
	}
	let historical = self.provider.state_by_block_hash(parent_hash)?;
	Ok(MemoryOverlayStateProvider::new(in_memory, historical))
	}

this we need keep in the State so we can easily serve it

reth/crates/engine/tree/src/tree/mod.rs

Lines 1015 to 1017 in 8c8702b

	/// State after applying the given block.
	#[derive(Debug, PartialEq, Eq, Clone)]
	pub struct State(ExecutedBlock);

this will be accessed a lot concurrently, so we need to be careful we keep the mapping right, which is updated when we flushed to disk.

This can now be integrated into the Blockchainprovider2 state_by calls