enhance GetBlockByNumber by supporting 'safe' and 'finalized', following Geth

[NathanBSC]

Description

enhance GetBlockByNumber by supporting 'safe' and 'finalized', following Geth

Rationale

1. follow up with Geth, to improve user experience, 'finalized' and 'safe' meaning, refer to
   https://www.alchemy.com/overviews/ethereum-commitment-levels
2. transplant code from Geth,
   and the binding position is CurrentFinalBlock() and CurrentSafeBlock()
3. remove GetFinalizedHeader and GetJustifiedNumberAndHash in ethapi list

Example

have been tested
curl -X POST "http://127.0.0.1:8545" -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}'

curl -X POST "http://127.0.0.1:8545" -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["safe", true],"id":1}'

curl -X POST "http://127.0.0.1:8545" -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["finalized", true],"id":1}'

Changes

Notable changes:

• add each change in a bullet point here
• ...