feat(guild): add fetch_role

[spifory]

Summary

• Implements Add Get Guild Role endpoint discord/discord-api-docs#7074

Tested with

from nextcord import Intents, Interaction, Role
from nextcord.ext.commands import Bot

bot = Bot(
    intents=Intents(guilds=True, message_content=True, messages=True),
    default_guild_ids=[...],
)

@bot.slash_command()
async def role(inter: Interaction, role: Role):
    assert inter.guild is not None
    fetched_role = await inter.guild.fetch_role(role.id)
    return await inter.send(repr(fetched_role))

bot.run(...)

This is a Code Change

• I have tested my changes.
• I have updated the documentation to reflect the changes.
• I have run task pyright and fixed the relevant issues.