refactor(core): remove attohttpc client, closes #6415

[lucasfernog]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

[FabianLars]

fwiw i really agree with this change 😅 If we need more reasons to merge this PR, here are the first two things i found in my todo list:
https://discord.com/channels/616186924390023171/1031003062774542426/1031230486527352912 (corrupt deflate stream)
https://discord.com/channels/616186924390023171/1074836726230548551 (attohttpc causing issues in the updater, don't know specifics)

Also it will probably make adding cookie support easier (since reqwest has built-in support)
and most rust devs use reqwest which caused binary bloat because our reqwest-client flag wasn't documented good enough - tbh i wouldn't know how to solve this with docs alone, why/where would people look for that in the first place...