Improve mining loop to reduce coupling in operations between miner and daemon

[shrenujbansal]

Checklist

• This is not a new feature or an enhancement to the Filecoin protocol. If it is, please open an FIP issue.
• This is not a new feature request. If it is, please file a feature request instead.
• This is not brainstorming ideas. If you have an idea you'd like to discuss, please open a new discussion on the lotus forum and select the category as Ideas.
• I have a specific, actionable, and well motivated improvement to propose.

Lotus component

• lotus daemon - chain sync
• lotus miner - mining and block production
• lotus miner/worker - sealing
• lotus miner - proving(WindowPoSt)
• lotus miner/market - storage deal
• lotus miner/market - retrieval deal
• lotus miner/market - data transfer
• lotus client
• lotus JSON-RPC API
• lotus message management (mpool)
• Other

Improvement Suggestion

The current mining loop causes a lot of coupling between the miner node and the chain node.
Specifically, it selection of messages, block creation and block submission are all different APIs from miner to daemon which are required to hit the same daemon node
Such coupling results in a lot of back and forth requests between processes and poses several challenges in scaling both miner and daemon nodes, not to mention that we got here due to historic reasons

We need to investigate how to properly decouple/consolidate these APIs