Implement simple async worker for PoA sealing engine

[jangko]

This issue will function as a reminder for me to consolidate various elements and form a working sealer. The goal is to pass clique smoke test of hive, and later will be used in rpc tests of hive after the txpool completed.

Requirements:

• legacy gasLimit, EIP-1559 gasLimit, EIP-1559 baseFee, from EIP-1559: Fee market change and London #741
• async tick event will use simple async timer combined with cliquePeriod from add new command line options: clique-period, engine-signer, and impor… #777
• the sole signer, taken from config: fix config file parser #787
• PoA validator from Feature/implement poa processing #748 and [BUMP] bump json rpc #745
• Tx Pool will come later if it's ready, fow now we can omit Tx Pool, but should contains a working tx execution accompanied by a test.
• uncles can be omitted to simplify the initial implementation and can be added later.
• async lock/guard can be omitted for simplicity, and can be added later if it interfere with block sync