feat: introduce safe and finalized as block number filters

[Stefan-Ethernal]

Description

The PR introduces finalized and safe keywords for block numbers in the JSON RPC layer. Because of the instant finality and there are no reorgs, safe and finalized behave the same way as the latest (namely the latest block from the store is returned).

Also, values are aligned with those used in the Ethereum spec (https://docs.tatum.io/docs/evm-block-finality-and-confidence#block-tags-and-their-meanings). See ethereum/go-ethereum#25165.

const (
	SafeBlockNumber      = BlockNumber(-4)
	FinalizedBlockNumber = BlockNumber(-3)
	LatestBlockNumber    = BlockNumber(-2)
	PendingBlockNumber   = BlockNumber(-1)
	EarliestBlockNumber  = BlockNumber(0)
)

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)