Add helper functions for refitting decays

This MR adds the function (and test) to refit a full decay tree with a single function, effectively enabling this piece of code to work:

    my_particles = get_particles("/Event/HLT2/Hlt2Charm_DpDspToKmPipPip/Particles")
    refitted_decay_tree_result = track_refitting.refit_decay_tree( input_particles=my_particles )
    refitted_decay_tree = refitted_decay_tree_result.OutputParticles

It relies on the functionality introduced in Rec!3995 (merged) and should be merged together.

Undrafted when also a test is adapted to use this.