feat: implement __eq__ between BaseFlags and flag_values

[Sharp-Eyes]

Summary

This PR adds support for __eq__ comparison between BaseFlags and flag_values.

For example,

>>> disnake.Intents(guilds=True) == disnake.Intents.guilds
True

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, ...)

[Enegg]

I think this could go a step further and make BaseFlags.flag simply return an instance of BaseFlags
Thoughts?

[Enegg]

See Enegg@2cbd98e

[shiftinv]

I think this could go a step further and make BaseFlags.flag simply return an instance of BaseFlags
Thoughts?

@Enegg Yea, this has come up once or twice, it would be a good thing in the long run. In an ideal world, flags would probably just be a special type of enum, like they are in the stdlib.
I want to avoid changing this in 2.x in case anyone is somehow relying on this, but it could be a good starting point for a potential refactor in 3.0 (or just a standalone change), if you'd like to PR your branch.

[shiftinv]

lgtm, thanks!