workaround issue 7702 and import wraps where needed

see issue #7702 
After looking at this for a bit It seems there are two places for a hash based-bug to rear its head.

1.  `SingleContinousDistribution.compute_cdf` is initialized differently according to the order of `kwargs`

2.  The order of substitutions in subs.  

The second option is an easy fix since we can just use a tuple instead of a dict for the subs to control the order (maybe that's what you actually proposed earlier but I don't remember).