fix(commands): some caveats related to guild cache in user app interactions

[shiftinv]

Summary

The other remaining part of #1173.
This adds a small note to Interaction.member, explaining why role-related fields might not work in certain situations. This was already more or less present on Interaction.guild, but the internal relationship between those isn't immediately obvious.
Also makes the @commands.dm_only and @commands.guild_only checks work properly in all cases by using guild_id instead of guild for interactions, additionally adding a note linking to the better alternative (ie contexts).

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, ...)