[ETCM-987] Fix saving the best block number without adding a mapping between block number and block hash

[leo-bogastry]

Description

Calling appStateStorage.putBestBlockNumber that makes an update to the best block number without calling blockNumberMappingStorage.put to add the mapping between the block number and block hash can result on a None when calling blockchain.getBestBlock.
I wanted to add these two calls together in the blockchain or blockchainwriter class, but it is not that straight forward.

In order to be able to test this modification already I applied the fix in FastSync and created ETCM-1089 for a proper refactor

Testing

This has been tested against mainnet.

[jvdp]

I don't disagree with this change but I feel the main improvement it does is mention the TODO in the code that this logic needs to move to a blockchain-storage related component. It won't affect the actual bug because that doesn't have much to do with fast sync, as discussed.

[leo-bogastry]

I don't disagree with this change but I feel the main improvement it does is mention the TODO in the code that this logic needs to move to a blockchain-storage related component. It won't affect the actual bug because that doesn't have much to do with fast sync, as discussed.

I think you are probably right. The modification shows that is was not just about having cache and storage in synchronization, different storages should also be always syncronized