Lots of repeated code in model.py

[barkls]

You have separate functions with and without laser skew but much of the code is duplicated between them. Either consolidate the functions into a single shared workflow or break out the duplicated code into helper functions that are called by both.

[ssghosh]

Broke out the sampler code from Walkers and laserskew_Walkers into a helper function walkers_sampler in 97cd8c3