WIP: Make SEOBNRv3_opt more robust than SEOBNRv3

This patch combines SEOBNRv3_opt's two integration routines into a single routine. This single integration routine has two parts. The first part is the same as the first of the two original integrations; the second part backsteps 150 M in time, decreases the ODE tolerance, and then reintegrates until the stopping condition is satisfies. This second part replaces the second of the two original integrations. The more strict ODE tolerance results in more precise ringdown attachment, and improves faithfulness between v3_opt and v3_opt_pert.