Use step scale in the valueCallback()

Currently we do not use it so very big numbers might be malformed when cast to string. The reason is that converting from scientific notation you might get a number with up to 10 fractional digits and then saving it in a database it will round the number according its own settings.

Though being very rare case we need to ensure that number has the same quantity or less fractional digits as the field's step property. Just to avoid surprises.