The Incapacidad node in the nomina 1.2 complement had two issues
preventing CFDI stamping for payslips with IMSS incapacity leaves:

1. The ImporteMonetario attribute was missing entirely. This is a
   conditional attribute defined in the SAT XSD (nomina12.xsd) to
   express the monetary amount of the incapacity. Without it, the
   SAT rejects the CFDI with validation error NOM95:
     'El atributo Deduccion:Importe no es igual a la suma de los
     nodos Incapacidad:ImporteMonetario, ya que la clave expresada
     en Nomina.Deducciones.Deduccion.TipoDeduccion es 006.'

2. The DiasIncapacidad attribute was rendered as a float (e.g. '11.0')
   instead of an integer ('11'). The XSD defines it as xs:int with
   minInclusive=1, so the float representation caused error 301
   (XML mal formado).

Per the SAT filling guide, the ImporteMonetario value depends on
the context:
- Default: the amount comes from deduction 006 (Descuento por
  incapacidad), which is the discount applied to the worker.
- Exception: when perception 014 (Subsidios por incapacidad) exists,
  the amount comes from that perception instead, representing the
  subsidy paid to the worker.

When neither deduction 006 nor perception 014 exist on the payslip,
the attribute is omitted (None) to comply with its conditional
nature in the XSD.