fix(assets): replace .gif asset format to webp for animated assets

[SilberGecko6917]

Summary

This PR changes the .gif asset extention for avatars, banners and other images to the .webp extention.

https://docs.discord.com/developers/reference#image-formatting

I noticed that if a user had an animated profile picture, the URL of the image returned a 415 Unsupported Media Type error. For example, here:
https://cdn.discordapp.com/guilds/1010915072694046794/users/851762178532311050/avatars/a_8a63bc5a3a227954876eb04778006c13.gif?size=1024

but with webp it works:
https://cdn.discordapp.com/guilds/1010915072694046794/users/851762178532311050/avatars/a_8a63bc5a3a227954876eb04778006c13.webp?animated=true&size=1024

I used claude (https://claude.ai/) to check over my code and get some help with how i could fix the issue.

Information

• 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, typehinting,
  examples, ...).
• I have read the Contributing Guidelines .

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.
• AI Usage has been disclosed.
  • If AI has been used, I understand fully what the code does

[pycord-app]

Thanks for opening this pull request!
Please make sure you have read the Contributing Guidelines and Code of Conduct.

This pull request can be checked-out with:

git fetch origin pull/3294/head:pr-3294
git checkout pr-3294

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3294/head

[Lulalaby]

@Paillat-dev

[Paillat-dev]

I have the feeling that this PR is changing too much, but haven't had the time to take a look in depth. I will check it out asap.

[Paillat-dev]

Wait for my review

[Paillat-dev]

Why was this added, as well as extension, as attributes ?

Adding size here seems kind of an unrelated change.

Please do something similar to 89cd452

Where a simple extension @\property was added with something like if self.animated ... else .... And default to webp for animated and png for not.

Also why did you add this:

if animated:
    url += "&animated=true"

Independently of the reason, it again seems unrelated. Either change the scope of this PR or remove unrelated changes.

[vmphase]

with_query replaces the entire query string rather than merging into it. See the discussion.

Suggested change

	url = str(yarl.URL(self._url).with_query(size=size))
	url = yarl.URL(self._url).with_query(size=size)
	if self._animated:
	url = url.update_query(animated="true")
	url = str(url)