chore: use iterator findall over traverse

[CoderJoshDK]

Summary

RE #1441 (comment)

docutils deprecated the use of traverse in place of findall. They are essentially the same function. But one returns an iterator and the other a list.

This PR changes the code to use findall and makes docutils an explicit docs dependency (you are using it explicitly, you should require it explicitly)

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 uv run nox -s lint
  • I have type-checked the code by running uv run nox -s 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, ...)

[read-the-docs-community]

Documentation build overview

📚 disnake | 🛠️ Build #30020140 | 📁 Comparing 094cd92 against latest (13d648e)

🔍 Preview build

Show files changed (48 files in total): 📝 48 modified | ➕ 0 added | ➖ 0 deleted

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index.html	📝 modified
whats_new.html	📝 modified
api/abc.html	📝 modified
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ext/commands/api/prefix_commands.html	📝 modified

[shiftinv]

lgtm, thanks!