[Proposal] Update finalize_root derivation

[raychu86]

Motivation

This PR explores a new method of deriving the finalize root. Instead of using FinalizeOperations to create a tree and find the root, we use the FinalizeStore atomic_write_batch instead. We simply hash it to construct the new finalize_root (which can be renamed as it is no longer a root).

The finalize root is now derived when VM::speculate or VM::finalize is called, instead of being derived from the FinalizeOperation state in Transactions, which means we can safely remove FinalizeOperations entirely if desired.

Note: The FinalizeOperations have not been removed in this proposal, but will be removed if we decide to go down this route.

TODO: Resample genesis block

[ljedrz]

Suggested change

	$result.extend(key.to_bytes_le()?);
	key.write_le(&mut $result)?;

[ljedrz]

Suggested change

	$result.extend(value.to_bytes_le()?);
	value.write_le(&mut $result)?;

[ljedrz]

Suggested change

	$result.extend(key.to_bytes_le()?);
	key.write_le(&mut $result)?;

[ljedrz]

Suggested change

	$result.extend(value.to_bytes_le()?);
	value.write_le(&mut $result)?;

[ljedrz]

Suggested change

	$result.extend(key.to_bytes_le()?);
	key.write_le(&mut $result)?;

[ljedrz]

Suggested change

	$result.extend(v.to_bytes_le()?);
	v.write_le(&mut $result)?;

[ljedrz]

Suggested change

	let input = write_batch.iter().flat_map(|b| b.to_bits_le()).collect::<Vec<_>>();
	let mut input = Vec::new();
	for b in write_batch.iter() {
	b.write_bits_le(&mut input);
	}

[ljedrz]

Suggested change

	let input = write_batch.iter().flat_map(|b| b.to_bits_le()).collect::<Vec<_>>();
	let mut input = Vec::new();
	for b in write_batch.iter() {
	b.write_bits_le(&mut input);
	}