refactor: sort sophus more consistent into directory structure

[strasdat]

• sort cpp/sophus2 better into existing directory structure
  • moves cpp/sophus2/cpp/sophus -> cpp/sophus
  • moves cpp/sophus2/protos to protos/sophus
  • moves cpp/sophus2/docs -> docs
  • remove lots of unused scripts
• dependency management
  • document venv
  • merge / simply venv build scripts
• fix all build scripts CI to reflect the change

Note: This PR won't attempt to merge geometric protos from sophus with duplicates protos in the farm_ng namespace. This will be done in follow-up, while aiming to minimize log format disruptions.

[ethanrublee]

Looking great @strasdat Feel free to merge any time you are ready. Any missing clean up can be done as smaller PRs and looks like you've hit all your goals for this PR.