Groups a holdings read by instrument and sums it, spendable apart from locked.
sumHoldings([{ amount: '1.5', instrumentId, isLocked: false }])// [{ balance: '1.5', instrumentId, locked: '0' }] Copy
sumHoldings([{ amount: '1.5', instrumentId, isLocked: false }])// [{ balance: '1.5', instrumentId, locked: '0' }]
Groups a holdings read by instrument and sums it, spendable apart from locked.