Fixes RDT bug with Sparse Values and preps for test

- RDT doesn't like sparse values, they aren't handled the same way as a
   coverage handles them so now there is a spanify wrapper which manages
the span objects inside the storage.
- Certain parameter contexts are failing at creation time due to numpy
   not being JSON compliant, added a walker to convert them

TODO: Need to weed out NaN in the walker