The resummation was previously applied to all energy points when the flag was set, causing resummed and standard modes to differ everywhere. Per spec, it should only replace C(beta)*ln(W0-W) with the resummed power-law form when (W0-W) < delta_cut (~1e-3). Adds delta_cut parameter (default 1e-3) and corrects the resummation switch test to verify identical results far from endpoint.