MAINT: Push down declarations in _convert_from_list
MAINT: Push down declarations in _convert_from_list

This makes it easier to reason about which variables contain mutable state.
C99 makes some of this possible, while other parts were already possible.

endolith/numpy,anntzer/numpy,mattip/numpy,charris/numpy,mattip/numpy,madphysicist/numpy,WarrenWeckesser/numpy,pbrod/numpy,grlee77/numpy,charris/numpy,grlee77/numpy,mattip/numpy,mhvk/numpy,rgommers/numpy,pdebuyl/numpy,pbrod/numpy,mhvk/numpy,seberg/numpy,pbrod/numpy,abalkin/numpy,numpy/numpy,simongibbons/numpy,pbrod/numpy,grlee77/numpy,rgommers/numpy,seberg/numpy,simongibbons/numpy,seberg/numpy,simongibbons/numpy,WarrenWeckesser/numpy,rgommers/numpy,mhvk/numpy,rgommers/numpy,jakirkham/numpy,madphysicist/numpy,mhvk/numpy,WarrenWeckesser/numpy,pbrod/numpy,abalkin/numpy,madphysicist/numpy,anntzer/numpy,jakirkham/numpy,endolith/numpy,numpy/numpy,seberg/numpy,mattip/numpy,pdebuyl/numpy,jakirkham/numpy,endolith/numpy,pdebuyl/numpy,WarrenWeckesser/numpy,numpy/numpy,charris/numpy,anntzer/numpy,jakirkham/numpy,simongibbons/numpy,endolith/numpy,grlee77/numpy,WarrenWeckesser/numpy,pdebuyl/numpy,numpy/numpy,grlee77/numpy,anntzer/numpy,charris/numpy,abalkin/numpy,simongibbons/numpy,madphysicist/numpy,mhvk/numpy,madphysicist/numpy,jakirkham/numpy