Consider support of big numeric types

[jjttjj]

It's currently unclear if the big numeric types (bigdec, bigint, etc) should supported as domain or range values. My recent commit 555a6a9 doesn't support these types.

At some point it should be decided to either support these types in the core wadogo.scale functions, and if so test them. Otherwise make it clear they are unsupported.

It's worth considering if there are valid cases to scale big numbers. There also may be a performance impact to support them.