BUG: SampleData[AlphaDiversity] -> Metadata doesn't work with tuples

[thermokarst]

Bug Description
Some SampleData[AlphaDiversity] Artifacts contain tuples of numbers (for example, chao1). The transformer to qiime2.Metadata explodes when it sees this.

Steps to reproduce the behavior

1. Produce a Chao1 SampleData[AlphaDiversity] Artifact.
2. qiime metadata tabulate --m-input-file chao1_ci.qza --o-visualization chao1_ci.qzv
3. See error

Expected behavior
Transforming SampleData[AlphaDiversity] to Metadata should work.

Questions

1. Do we solve this in the transformer, or the format, or both, or neither?

References

1. Originating forum post

[thermokarst]

This is an old issue, and one I suspect has been documented somewhere else, so if we ever find the xref, let's merge here into this issue.