chore(deps): Sort requirements files

[BobDotCom]

Summary

This PR categorizes requirement files into a requirements/ directory.

Information

• 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, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.

[EmmmaTech]

Why is the main requirements file just named _.txt? Either move the file outside of the requirements folder or name the file main.txt.

[BobDotCom]

I took inspiration for this layout from another project, and I've been wanting to implement it for a while but only just now got to it. Not sure which project, but they used _.txt and that's why this uses it. I don't particularly see any reason against it though.

[Lulalaby]

merge conflicts