Confirmation blocks to include block number

[buckyroberts]

Add block_number to confirmation blocks. This will simplify synchronization across nodes and also allow us to use our updated time model which is based on block_number.

We also need to keep the most recent block_number in cache, similar to how we do for HEAD_BLOCK_HASH. This is because the system will need to know that value in order to increment it every time a new block is created.

HEAD_BLOCK_HASH overview

• https://thenewboston.com/guide/confirmation-validators

Confirmation block API docs

• https://thenewboston.com/primary-validator-api/confirmation-blocks
• https://thenewboston.com/confirmation-validator-api/confirmation-blocks

The resulting shape of a confirmation block would look similar to this.