Adjust for optional totalDifficulty in JSON-RPC BlockObject

[kdeme]

Going for optionally totalDifficulty instead of removal.

See reasoning in discussion here: #3882 (comment)

Depends on status-im/nim-web3#233

[kdeme]

I want to note that, ideally here getScore returns a None in case the block referenced is post-merge.

However from reading the code it would seem that is not the case (but it was probably the long term plan).

One could assume that getScore here would return failure if block post merge:

nimbus-eth1/execution_chain/db/core_db/core_apps.nim

Line 217 in 08efe95

if error.error != KvtNotFound:

But this comment indicates that the score is still stored also for each post merge block:

nimbus-eth1/execution_chain/db/core_db/core_apps.nim

Lines 606 to 613 in 08efe95

	# TODO it's slightly wrong to fail here and leave the block in the db,
	# but this code is going away soon enough
	return err(info & ": cannot get score")
	score = parentScore + header.difficulty
	# After EIP-3675, difficulty is set to 0 but we still save the score for
	# each block to simplify totalDifficulty reporting
	# TODO get rid of this and store a single value

I have not tested this yet but I would assume that it will still find a score.

[kdeme]

Using txFrame here for the fork-aware view, even though this value is not needed for current forks (post merge forks). I assumed it was useful also when using it for uncle blocks (pre-merge). But after looking into the code it is not. I will adjust to the baseTxFrame version.

[kdeme]

@bhartnett I think it is not needed to do the txFrame version as you have added here: https://github.com/status-im/nimbus-eth1/blob/bal-devnet-0/execution_chain/rpc/debug.nim#L119-L122

As this value is not supposed to change anymore. (and ideally does not get set post merge, but ok)

[bhartnett]

@kdeme Good point. In that case should it just always return zero?

[kdeme]

I will go ahead and merge this version as it is an improvement:

• same behaviour for TD for blocks that are available: This can be improved in the future for post-merge blocks. Either by changing the TD storage in the future, or by checking simply if it is a pre or post merge block number.
• blocks that are not found -> return none instead of the latest TD