Fix issues with tracing builds (#7809)

Fix issues with tracing builds (#7809)

This PR fixes two issues that were revealed when analyzing decreased performance on trace-enabled builds.
hasIntegerModel() turns out to be a rather expensive method and should thus not be called in a Trace output.
Furthermore, the implementation of Rational::isIntegral() was generally bad because it used getDenominator() (which returns a copy of the denominator as an Integer) instead of directly checking the underlying denominator with equality for zero.