WIP: Add better type definitions

[mattphillips]

This is a bit of a POC to add type definitions for each diff function that works correctly.

I've not exhaustively tested this yet so don't know if it covers all cases but the general idea is as follows:

• diff: Merge the left hand side and right hand side types into optionals at all levels and convert arrays to dictionaries (recursing on the inferred array element type)
• added: Keep all new RHS keys and set all old LHS keys to never. All new new at any level should not be optional. Arrays can also have been inserted into so they should be kept in the types but made optional dictionaries.
• deleted: Keep all keys that are not present on the RHS keys but exist in the LHS as undefined. Arrays can also have been deleted from so they should be kept in the types but made optional dictionaries.
• updated: TODO

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (8a8138f) compared to base (e37b759). Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #88   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            7         7           
  Lines          109       109           
  Branches        36        36           
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  Hits           109       109           

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