fix: support interactions in UserConverter/MemberConverter

[shiftinv]

Summary

Adds support for ApplicationCommandInteraction to commands.UserConverter and .MemberConverter. While slash commands don't use these converters and instead use the builtin option type, these converters may still be called manually.

^{Also improves the channel_types error message, which is somewhat but not really related. I just didn't feel like opening a separate PR for a change of a few characters}

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 task lint
  • I have type-checked the code by running task 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, ...)

[onerandomusername]

lgtm