Reduce code duplication for make*pulse

[mcencini]

I was thinking RF pulse codes are largerly redundant. We could maybe consider reducing most of these to thin wrappers around make_rf_arbitrary(), e.g:

def make_sinc_pulse(...):
    """docstring"""
    # no need to validate (most if not all) inputs: make_arbitrary_rf already does it
    
    # focus on signal array generation
    bandwidth = time_bw_product / duration
    alpha = apodization
    n_samples = round(duration / dwell)
    t = (np.arange(1, n_samples + 1) - 0.5) * dwell
    tt = t - (duration * center_pos)
    window = 1 - alpha + alpha * np.cos(2 * np.pi * tt / duration)
    signal = np.multiply(window, np.sinc(bandwidth * tt))
    flip = np.sum(signal) * dwell * 2 * np.pi
    signal = signal * flip_angle / flip

    return pp.make_arbitrary_rf(signal, ...) # pass through relevant args

thoughts? @schuenke

[mcencini]

If it is a good idea, it would probably good to slightly extend make_arbitrary_rf so it can also accept an optional time arg (similarly to make_extended_trapeziod) and to also optionally return the slice rephasing block gzr.