Return the millisecond value of rational at tempo.
abjad> from abjad.tools.quantizationtools import tempo_scaled_rational_to_milliseconds
abjad> tempo = contexttools.TempoMark((1, 4), 60)
abjad> tempo_scaled_rational_to_milliseconds(Fraction(1, 4), tempo)
Duration(1000, 1)
Return a Duration.