docs: add v2.9.1 changelog to latest docs

[shiftinv]

Summary

i forgor.
This is a copy of the changelog from stable docs to latest docs - one of the few parts of the release process that aren't automated yet, and probably won't be in the near future.

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[EQUENOS]

ok