Provide model quality metrics

Example metrics:

- domain coverage
- ratio of domain cardinality vs number of test cases
- cardinality is 2 for Bool, infinite for String, each argument multiplies the function cardinality
- _note:_ this serves the "make invalid state unrepresentable" guideline

The issue names no files, tests, or entry points. Start by locating the Morphir model and test-case code, then determine where model quality metrics would belong and how domain cardinality should be represented. Done means the requested metrics, including domain coverage and the stated cardinality rules, are defined and available with tests or documentation showing their results.

Written by the indexing model from the issue text.