[Liquidation improvements] Completely decouple MTM, margin checks and closeout trades

[gordsport]

Issue:

This issue is to implement liquidation improvements noted having seen markets working in mainnet since Alpha mainnet was deployed by the validators.

The current design around margins means that:

• closeout trades happen (or are attempted) when a party is in breach of margin requirement and when there is enough volume and when we're not in an auction.
• we cannot handle (future) frequent batch auctions
• we may reward a party that has a big position (MTM move against them, we want to close out but can't, MTM move for them they're OK again - the network was at risk but party kept profit).
• the logic in core is tightly coupled in places making moves towards WASM based smart products harder.
  The aim here is:

Separate margin checks, mark-to-market and closeout trades into three separate streams that can run at arbitrary frequencies,

1. Accommodate closeout trades during auctions,
2. Avoid allowing parties with huge position breaching margin level hanging around.
3. Do this without changing any existing margin calculations.
4. Do this without changing how loss socialisation works.

Specs:

• [Liquidation improvements] Completely decouple MTM, margin checks and closeout trades specs#1641