Metadetect won't run on only `noshear`

[sidneymau]

I was trying to do some quick metadetect tests in which only the noshear step is processed. However, when specifying this in the config, metadetect keeps processing both noshear and 1p. After tracing through the different calls, I suspect this is the cause: https://github.com/esheldon/ngmix/blob/d08b471f4c4d5887df9f9f2551efaf8f2e226150/ngmix/metacal/metacal.py#L146-L150

It would be very useful if I could run through the metadetect code (including detection & fitting) for just noshear for same tests of the detection & measurement pipeline, so I wonder if this can be updated?

[sidneymau]

I think the only change that would be necessary is to extract out the "get_unsheared" bit from https://github.com/esheldon/ngmix/blob/d08b471f4c4d5887df9f9f2551efaf8f2e226150/ngmix/metacal/metacal.py#L181-L185 and rather have the code run each requested type in sequence (rather than trying to do two at once in this unusual case -- or only doing this is if another shear type has been requested)