Cython compatibility

[Borketh]

Summary

This PR is supposed to fix some incompatibilities with Cython and Nextcord.
The first of these is that Cython stores coros internally with the same co_flags as a regular function. Since inspect.iscoroutinefunction is used a bunch in nextcord to ensure listeners work right, "Pure Python" compiled with Cython cannot use nextcord. Cython does add a flag elsewhere that asyncio.iscoroutinefunction does check for (see this). I replaced all calls to inspect's impl with asyncio's impl, altering imports where necessary.

This is a draft for now, because I don't want to merge it until I can make a bot using Cython. Once the first obstacle is fixed, I'm sure there will be more.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• 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, ...)

I don't know how to test this yet, I was wondering if you guys would be able to point me in the right direction

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[Skelmis]

lgtm

[ooliver1]

looks good so far, not approved as you said its untested, @ooliver#6969 in discord when tested though :)