On crab/dawwinia chain, max deposit time change to 12 months

[hackfisher]

As Crab SubDAO is involved more innovative exploration and subject to change, we should have less max deposit time just in case CRAB are locked/binded for too long time which could be expressed as reasons hinder evolution and innovation.

This just means the demand for CKTON will lead to more CRABs locked in shorter periods, nothing else changes essentially. Crab SubDAO, playing the role of canary in this community should act and explore paths more radically.

[hackfisher]

In future, long term, there could be multiple staking pools, pool for Ckton can be independent and separate, could have the same ratios as it is now.

Different from staking alone model, it can be switched SubDAO model, which means the CRAB tokens currently allocated to the staking pool can be seen as the Treasury buyback of the CKTON SubDAO, from the CKTON/CRAB liquidity pool. The bought CKTON can be burned or be used to create new LP-CKTON/CRAB like MakerDAO.

If it is a reasonable value exchange,the price paid for new buying back is the for the contribution of new CRAB Lock commitments, rather than a constantly income regardless of the SubDAO's contribution in currently status.

[aurexav]

Moved to solidity. cc @hujw77

[hackfisher]

Related gov proposal: https://github.com/orgs/darwinia-network/discussions/1603