message: fix(protocol-designer): cast offsetFromBottomMm values to number
  Some string values were being written to the the offsetFromBottomMm key of certain commands, this
  patch casts those values in the field level so that stepFromToArgs only receives numbers for tip
  position fields
diff: @@ -63,6 +63,9 @@ const stepFieldHelperMap: { [StepFieldName]: StepFieldHelpers } = {
  maskValue: composeMaskers(maskToFloat, onlyPositiveNumbers),
  castValue: Number,
  },
  + aspirate_mmFromBottom: {
  + castValue: Number,
  + },
  aspirate_wells: {
  getErrors: composeErrors(requiredField, minimumWellCount(1)),
  maskValue: defaultTo([]),
  @@ -84,6 +87,9 @@ const stepFieldHelperMap: { [StepFieldName]: StepFieldHelpers } = {
  maskValue: composeMaskers(maskToFloat, onlyPositiveNumbers),
  castValue: Number,
  },
  + dispense_mmFromBottom: {
  + castValue: Number,
  + },
  dispense_wells: {
  getErrors: composeErrors(requiredField, minimumWellCount(1)),
  maskValue: defaultTo([]),
  