Co-authored-by: Jackson Burns <[email protected]>

…object

here are all the solutions that were implemented:
 - in a couple places we were implicitly casting a double to a numpy float, now need to explicitly grad the _real_ part of the double
 - Cython does not allow nested function declaration inside cpdef functions, move all of these outside of their parent functions or redefine them to be purely functional where practical
 - similar to the above, lambda function are no longer allowed - get the same treatment. what's different here is that usually we are using lambda in sorting calls, so we can replace these with operator.itemgetter or attrgetter, where relevant. this also involves re-writing a couple reduce calls, which also used lambda
 - modern cython does not allow re-declaring existing Cython variables (in previous versions this was a warning I think), so I just remove these where needed. (btw Cython is super cool, actually points out both of the declaration so that you can delete one)

i made these fixes while listening to The Metal by Tenacious D, Talk Too Much by Renee Rapp, BEST INTEREST by Tyler, The Creator (love the bass line), mos thoser by food house, and Doritos & Fritos by 100 Gecs

as requested in: #2687 (comment)

want to see if the problem comes up again elsewhere

…ator/RMG-Py into feat/py39

for some reason `functools.partial` is allowed, but not `lambda`

…ator/RMG-Py into feat/py39