Add complex32 and bcomplex32

[hawkinsp]

We'd need this for 16-bit FFTs in JAX: jax-ml/jax#17954

[leofang]

@hawkinsp @jakevdp @seberg @kmaehashi We already had a draft PR to add cupy.complex32 (cupy/cupy#4454) which is made as a legit numpy.dtype via NumPy C APIs (CuPy only uses NumPy dtypes; it does not have its own dtype system). My preference (speaking from NVIDIA perspective) is to add exotic NumPy dtypes to ml_dtypes and encourage all projects to use them. What would be the needed ingredients for me to migrate that PR over to here? Is there a guidance that I can follow along?

[jakevdp]

I don't think there's any guidance beyond using the existing definitions in this repo as a template.

[matteoguarrera]

Hey @leofang I am working on that as well! I can help. Dropping an email right now!
Pytorch does have complex32