Apply Lorentz correction after binning into `(d, theta)`?

In scipp/essdiffraction#29 the Lorentz correction is computed in event mode and applied to the data. I think a cheaper approach would be something like:

data = data.bin(dspacing, theta)  # no more pixels, or data.groupby(theta).bins.concat('pixel')
lorentz_factor = sc.midpoints(dspacing)**4 * sc.sin(sc.midpoints(theta))
scale = lorentz_factor / vanadium  # vandium depends only on dspacing
data *= scale

This would result only in a single event-data op (which we would have to do anyway for the vanadium normalization). Binning in theta would have some extra cost, but we may need it anyway for other purposes. Computation of the Lorentz correction itself would essentially be free, and independent of the event count.

Start with scipp/essdiffraction#29 and compare its event-mode Lorentz correction with the proposed binning into dspacing and theta. Investigate whether the binned approach remains valid alongside vanadium normalization and measure its cost. Done means the project has a decided approach and an implementation or documented rejection backed by relevant comparisons.