initial state shape mismatch with emcee
https://git.ligo.org/lscsoft/bilby/-/blob/master/bilby/core/sampler/emcee.py#L332 in bilby requres the shape for initial state of emcee sample to be of shape=(ndim, nwalkers) when emcee expects shape=(nalkwers, ndim)
switching the order of that tuple should solve this issue and allow bilby to pass the correct pos0 to emcee