fix(emoji): turn Emoji.is_* properties into methods

[shiftinv]

Summary

Runtime changes split from #1388. These changes are for consistency with other existing code:

• is_app_emoji and is_guild_emoji are now methods instead of properties
• Non-route parameters to HTTPClient methods are now kwarg-only

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 #29726363 | 📁 Comparing d380873 against latest (eff6ca6)

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Show files changed (49 files in total): 📝 49 modified | ➕ 0 added | ➖ 0 deleted

File	Status
genindex.html	📝 modified
index.html	📝 modified
whats_new.html	📝 modified
api/abc.html	📝 modified
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api/emoji.html	📝 modified
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