breaking, fix: guild_member state tracking

[braindigitalis]

• breaking, fix: guild_member state tracking.
  You must now use add_role, remove_role or set_roles, also set_nickname on a guild_member for edit_guild_mebmer to have any effect on that value. This fixes longstanding issue where more permissions are required than should be, to edit guild members
• test: move mutltiheader cookie test to extended, impossible to test in uk and eu due to GDPR

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[Mishura4]

Requested changes + making the fields private as we discussed on Discord, and good for me

[Jaskowicz1]

Bellissimo.

[Mishura4]