Adapt kinetmatic limits of `ForElectronPositron`

[Jean1995]

The parametrization ForElectronPositron, i.e., the creation of an electron-positron pair by an ingoing electron or positron, currently uses the kinematic limits from the corresponding parametrizations for muons, i.e., KelnerKokoulinPetrukhin.

Since those kinematic limits are motivated by ideas not applicable to this parametrizations, one should use different kinematic limits here, e.g., v_min = 2m/E, v_max = 1 - m/E, rho_max = 1 - 2m / (v*E)