Change timestepping structure in run_part (#176)

* first pass at changing the timestepping procedure

* clean up and fix output progress

* clean up code

* minor fixes

* fix compile error when camp enabled

* add camp pointers to timestep subroutine

* delete old code

* added variables for tracking progress

* fix timestepping for camp

* switch to time step index to avoid precision issues

* rename time step variables

* trigger GitHub actions

* incorporate suggestion regarding CAMP argument passing

* fix missing space