feat: ✨ Add Member.colours

[ToothyDev]

Summary

This PR adds .colours and .colors to Member in order to get the rendered role's colours including secondary and tertiary.
Member.colour also now points to this, using the primary color.

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, ...).

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.

[pycord-app]

Thanks for opening this pull request!
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This pull request can be checked-out with:

git fetch origin pull/3063/head:pr-3063
git checkout pr-3063

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3063/head

[Paillat-dev]

Nice change in general

[Paillat-dev]

tested; code lgtm

[Paillat-dev]

However hold for 2.8