improve `checkDeltaBalance`

[rognierbenoit]

checkDeltaBalance should take an extra parameter: an epsilon tolerance when checking balance delta.

This is to replace the ususal pattern:

await checkBalanceDelta(user.pkh, (d) => checkEqualEpsilon(d, -10, 0.02), async () => {
 ...
})

where checkEqualEpsilon is:

const checkEqualEpsilon = (value, target, epsilon) => Math.abs(value - target) < epsilon;

Hence the call below should be:

await checkBalanceDelta(user.pkh, -10, 0.02, async () => {
 ...
})