Don't try to do observed+expected limits in same job, but distinguish by i_limit_scan input, and only sig_limit output.
sig_limit_step -> 0.25.
Don't do limits on MC toys; sig strength = -2 for expected limit jobs on data.
"observed_" dropped in sig_limit branch names.
TemplateInterpolator not responsible for setting a's size.
Make A_bkg/sig in the fit namespace so they can be accessed post-fit; set_n_bins responsible for setting n_bins and vectors' sizes.