refactor(docs): move enum documentation to docstrings

[shiftinv]

Summary

This moves all¹ the previous enum documentation from the api/*.rst files into docstrings of their respective enum class, and uses autodoc for them instead. The point of this is allowing IDEs to show descriptions on enum members.

The built result isn't much different, with only a few minor changes:

• The order of attributes now inherently matches the source and api docs; this was already the case 95% of the time
• Minor whitespace/punctuation/grammar issues have been fixed, whenever I noticed them
• An unnecessary operations block on MessageType has been removed

The purpose of the sphinx extension is to hide the enum values, i.e. making enum member headers just category instead of category = 4, matching the previous docs.
It also patches _EnumValueBase.__repr__ to use the __str__ representation instead, which is what sphinx would've done automatically if we were using stdlib enums. This only affects how enum default values are rendered within signatures:

ref: #1188 (comment)

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, ...)

Footnotes

1. only AuditLogAction remains where it was, as it alone is ~1400-1500 lines of documentation (more than all other enums combined), and enums.py is already large enough ↩