feat: expose ReflectionProfileDoubleExponentialPseudoVoigt (TOF profile) to Python #117

Problem

libobjcryst provides a double-exponential pseudo-Voigt profile for time-of-flight neutron data, ReflectionProfileDoubleExponentialPseudoVoigt (ObjCryst/ReflectionProfile.h), but pyobjcryst does not bind it. src/extensions/reflectionprofile_ext.cpp only exposes ReflectionProfilePseudoVoigt, ReflectionProfilePseudoVoigtTCH and ReflectionProfilePseudoVoigtAnisotropic.

Other TOF support is already available from Python (the WAVELENGTH_TOF enum, PowderPattern.ImportPowderPatternTOF_ISIS_XYSigma, and the internal TOF intensity correction), so the missing profile is the main thing preventing TOF Rietveld refinement from Python. Currently the only way to use it is to load a ReflectionProfileDoubleExponentialPseudoVoigt tag via XMLInput.

Proposed solution

Add a class_<ReflectionProfileDoubleExponentialPseudoVoigt, bases<ReflectionProfile>> binding in reflectionprofile_ext.cpp, following the same pattern as the ReflectionProfilePseudoVoigtTCH binding added in #115:

• constructors () and (const UnitCell&)
• CreateCopy
• SetProfilePar(instrumentAlpha0, instrumentAlpha1, instrumentBeta0, instrumentBeta1, gaussianSigma0, gaussianSigma1, gaussianSigma2, lorentzianGamma0, lorentzianGamma1, lorentzianGamma2) with keyword args

Add tests that

• construct the profile and assign it with PowderPatternDiffraction.SetProfile
• check that the refinable parameters are visible by name
• check that a TOF pattern computed with it is non-zero and changes when a profile parameter changes