Custom settlement periods

To allow better prices for large trades, we will enable MMs to define a custom settlement period - allowing them to bid on trades where liquidity may not be instantly available.

In Fermi v2, we'll be building additional features to further maximise the flexibility in liquidity provision by market makers- Firstly, we will allow trades to be set up with any settlement period, between a few seconds, up to 24 hours - allow makers to opt for t+1 day settlement, which may be particularly useful for larger trades where liquidity may not be readily available (it may be locked up on other platforms, or even other chains/exchanges). To allow the implementation of custom settlement periods without undue losses to takers, we're also devising a system of taker rebates, linked to any price movement in the settlement period. This will ensure that opting for trades with delayed settlement does not expose the taker to negative price movements during the settlement periods. The rebate will be paid by the maker, out of the profit that they have made from any price movement in the interim period.