ENH: write denoising stats to artifact

[ebolyen]

fixes #79 This was more work than I expected. Some things that might improve this in the future:

• Metadata seems like an obvious "super format". Is there a good way to indicate what columns are meant to be present and auto-generate a format from that?
• Framework could have transformers built in for Metadata and sub-formats
• reading/writing TSV files is still a frustrating experience, and there's probably still a million holes. Can we use the above ideas to create a generic and robust parser?

TODO:

• [x] all the tests are borked.

[thermokarst]

I can take a stab at testing and getting the PR finalized. Probably later today (?) 🙏 .

[thermokarst]

If my tests and other changes look okay to you @ebolyen, feel free to hit that "Squash and merge" button! ⏭

[ebolyen]

Thanks @thermokarst!