Consider adding `:success` as an "anomaly" category

[dgr]

A :success is not strictly an "anomaly," but it signals the absence of an anomaly when a map might be the natural return type from a given function. A model for this might be HTTP status codes, where 2xx codes indicate success, and then other categories are broken out by other first digit of the code (e.g., 1xx, 3xx, 4xx, 5xx, etc.).

The alternative to this is to first test a map for the absence of ::anom/category and then dispatch on ::anon/category. Having a :success category allows for a single test or type of test (e.g., using case).

If the idea that :success might be an "anomaly," then an alternative name might be :none.