Add a checksum to the top-level output of rank_collection

[chrysb]

It would be helpful to be able to see a checksum of the traits used to generate rarity so that publishers can compare to each other and see that we all used the same input to generate our ranks.

Describe the solution you'd like

result = RarityRanker.rank_collection(
   collection=collection
)

// result.checksum - string 
// results.ranked_tokens - the original array

The checksum would be generated from an alphabetically (ascending) sorted array of all of the attributes that will be included for ranking (e.g. numeric traits would be omitted)