This can be sorted, making updating them more lightweight because
diffs are smaller and probably also GIT's delta compression works
better.

Suggested by @zesoup.

It is now down to the 20% of the old type system.

This allows modelling type compatibility beyond equality.

Override for table_sample.

It now returns something other than int when the type is not
constrained.

Previous implementation used a bit too much brute force and caused
excessive retries.