[ENH] support Serepent 2.2.1

[rzehumat]

Closes #480

Make sure you have read over the developer guide to ease the review process. These include:

• [x] PR fits the project scope
• [x] Code to be committed is DRY and matches the code style of the project
• [x] New and/or changed features are well documented and have adequate testing
• [x] For first-time contributors, you have included your attribution in docs/contributors.rst

Include a thorough and concise overview of the changes, and why this PR is overall beneficial to the project.

Once the PR has been created and is nearing closure, make sure that serious changes, including deprecations and incompatible changes are documented in the changelog

[rzehumat]

Check MapStrVersions (tick if it's unchanged since 2.1.29)

• [x] meta
• [x] rslt
• [x] univ
• [x] days
• [x] burnup
• [x] infxs
• [x] b1xs
• [x] varsUnc

[rzehumat]

Ok, I think it's ready for review, @drewejohnson

• It only adds 2.2.1 to supported versions.
  • I've quickly checked with the changelog and 1 _res.m file... If more testing is needed, let me know.
  • This changed only 2 files
• The remaining ~29 changed files result from running codespell to check for typos

[rzehumat]

Now I'm unsure why I see "Changes requested" here. I thought your change request is resolved.

[drewejohnson]

Now I'm unsure why I see "Changes requested" here. I thought your change request is resolved.

It's just because the last review had changes requested. You applied them, and it looks great!