Clean up RDRS conversion module, create io module

[Zeitsperre]

Pull Request Checklist:

• [ ] This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• [ ] Tests for the changes have been added (for bug fixes / features)
  • [ ] (If applicable) Documentation has been added / updated (for bug fixes / features)
• [ ] HISTORY.rst has been updated (with summary of main changes)
  • [ ] Link to issue (:issue:number) and pull request (:pull:number) has been added

What kind of change does this PR introduce?

• Splits setup code from rdrs modules into a template
• Static typing
• Refactored out several function-like blocks of code, apply existing functions where possible

Does this PR introduce a breaking change?

No (everything was already broken).

Other information:

[Zeitsperre]

@tlogan2000

I'm working my way through this, and it seems clear that we need an IO-handling module (similar things have been discussed for xscen). Do you have time to go over this with me? I'm going to try and pull out as much of the output-setup and file-writing code into their own functions and see whether I can integrate them into existing workflows and generalize them for multiple projects.

I also think it's time to create some development documentation to answer a few questions:

• What corrections go where?
• How do we gather files?
• How do we line up jobs to be computed?

One approach that came to mind would be writing a wrapper for performing the setup for writing out files (gathering files, checking for tempfolder, etc.) so that users don't need to rewrite it all the time.

Ideally, I want to remove these monolithic conversion functions that have been rewritten 3–4 times now under various names.