Define public type for data storage in RichCKResolutionFitter::FitParams

Seemingly minor change that helps to address access to some types from python

pcmf ~/LHCbCMake/Feature/Panoptes/output > python
Python 3.9.12 (main, Oct 19 2022, 15:11:58) 
[GCC 12.1.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from GaudiPython import gbl
>>> fitter = gbl.Rich.Rec.CKResolutionFitter()
>>> print(fitter.params().RichStartRes)
{ 0.00085000000, 0.00053000000 }