MuGirl - make functions called in execute const

Hi,

this MR makes several of the functions inside the MuGirl packages that are called during execute const. Remark for the shifters: the MuonRecoValidationTool is a not thread safe tool which can be added for validation/debugging checks when running with one thread. It is not included in multi-threaded production jobs, so not making it thread-safe here.

Best, Nico