Constructs a slippage override.
accountId and accountGroupId are mutually exclusive. slippageBps
is the override slippage in basis points, or null/undefined to defer
to the next cascade tier.
Throws ParamError when both accountId and accountGroupId are set.
Slippage override applied at one tier of the spot-funds cascade.
accountIdandaccountGroupIdare mutually exclusive; setting neither targets the instrument default. Resolution order is (instrument, account) -> (instrument, group) -> instrument -> global.