adding HWP support to OpSimConviqt.

[giuspugl]

The approach that we are following here is to slightly modify the convolution function and add the extra angle from the HWP to the polarization angle prior to the interpolation of the data cube, to get the observed signal in a given TOD sample.
we convolve three streams, one for intensity, one for perfectly co-polarized beam and one for a perfectly cross-polarized beam and finally we coadd them.

[giuspugl]

I have updated the weights for the polarization angles consistently as it is now in

toast/src/toast/todmap/pointing.py

Line 36 in 2a24945

d = cal \\left[\\frac{(1+eps)}{2} I + \\frac{(1-eps)}{2} \\left[Q \\cos{2a+4w} + U \\sin{2a+4w}\\right]\\right]

see

https://github.com/giuspugl/toast/blob/04957d2bee54172f0d8e679947876daeb5b2b2ec/src/toast/todmap/conviqt.py#L529

and

https://github.com/giuspugl/toast/blob/04957d2bee54172f0d8e679947876daeb5b2b2ec/src/toast/todmap/conviqt.py#L578

[tskisner]

Looks good to me, will merge it shortly