Add dual-simplex callback and reset root LP bound at solve start

- Set dual_simplex_objective_callback on lp_settings before root solve to
  populate root_lp_current_lower_bound_ during dual-simplex iterations
- Reset root_lp_current_lower_bound_ to -inf at beginning of solve() with
  solver_status_, is_running_, etc. to avoid stale bound on reused solver

Author: anandhkb