[RF] Use RooRealVar::setValFast() in minimizer interface

The `setVal()` function has the overhead of checking if the parameter
value is in the valid range. This is expensive, and it is the
responsability of the minimizer like Minuit 2 to only evaluate points
that are withing the defined parameter range.

Author: guitargeek

roofit/roofitcore/inc/RooRealVar.h

@@ -138,6 +138,8 @@ class RooRealVar : public RooAbsRealLValue {
   static bool _printScientific ;
   static Int_t  _printSigDigits ;
 
+   friend class RooAbsMinimizerFcn;
+
    void setValFast(double value) override
    {
       if (_value != value) {

roofit/roofitcore/src/RooAbsMinimizerFcn.cxx

@@ -234,7 +234,7 @@ bool RooAbsMinimizerFcn::SetPdfParamVal(int index, double value) const
       if (cfg().verbose)
          std::cout << par.GetName() << "=" << value << ", ";
 
-      par.setVal(value);
+      par.setValFast(value);
       return true;
    }