DOC/PERF: Decide how to handle floating point artifacts during rolling calculations
Currently we have a check here that artificially handles a numerical precision issue in `rolling.var` and `rolling.std` where our rolling variance calculation is carrying forward floating point artifacts. Ideally we should be using a more numerically stable algorithm (maybe Kahan summation) so this check isn't so arbitrary. 

https://github.com/pandas-dev/pandas/blob/601eff1768380313ec452ba8677cc7e825706796/pandas/_libs/window/aggregations.pyx#L305 