feat(role): add is_gradient and is_holographic properties

[ImChill1n]

Summary

Adds Role.is_gradient and Role.is_holographic properties based on Discord's role styling behavior.

According to the API:

• Roles with only primary_color are basic, without styling.

• Adding secondary_color makes the role a gradient.

• Adding tertiary_color turns it into a holographic style.

These properties check role style and reflect official Discord API behavior.

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, ...)

[ImChill1n]

Noticed the CI is flagging issues from files I haven’t touched. Looks like some type checks are running across the whole repo. My changes passed the relevant tests and are isolated to role.py.

[onerandomusername]

I'm not sure what happened, but somehow you had the entire repository copied within itself, and that's why tests and checks were failing. I've reverted the commits that cloned the entire repository, let me know if there's anything I can help with.

[ImChill1n]

I have removed both methods and replaced with enum and style, now distinguishing custom and holographic gradient.

[Snipy7374]

This is not consistent with the library, there's no need to introduce a new enum just for this. We usually add new enums for literal values coming from the discord API.

[ImChill1n]

Reverted Enum changes, I have added 2 methods back. I think current version should be good.

[Enegg]

I don't know about using the word "custom" here, it implies the existence of non-custom gradient