Code refactoring for `token` selection in `selection.py‎`

[talagayev]

Is your feature request related to a problem?

Following the discussion in #4790

Currently in selection.py‎ we have various tokens in individual classes, with all of them reusing certain functions like _apply() with small changes.

Describe the solution you'd like

A preferred approach would be to create a helper function Selection._apply_mathc_by_resname() that would be used, instead of reusing __apply()

This would result in something along the lines of:

def _apply(self, group):
    return self._apply_match_by_resnames(self.sugar_res)

Describe alternatives you've considered

Don't refactor the code and continue reusing __apply()

[Aryaman-Chaudhri]

Hi @talagayev , I have started to work on this , it seems like the given classes needs to be refactored ProteinSelection ,WaterSelection, NucleicSelection , BackboneSelection , NucleicBackboneSelection , BaseSelection , NucleicSugarSelection , will update shortly .