Margin and collateral

Add collateral to lower leverage or take collateral out.

await zeus.trade.addCollateral({ market: 'ETH/USD', side: 'long', amount: '0.05', payToken: 'ETH', slippage: 0.5 })
await zeus.trade.removeCollateral({ market: 'ETH/USD', side: 'long', amountUsd: 50, receiveToken: 'ETH', slippage: 0.5 })

Adding collateral is an increase request with size zero; removing it is a decrease request with size zero. Both wait for the keeper and return a receipt. Removing collateral raises leverage, and the Vault refuses a withdrawal that would take the position past 50.2x.