True-up the `invites` module

[null-domain]

Noticed a few discrepancies while working on #2212 / #2224 -

• invites.Invite is missing an enum field for all the possible invite types.
• While not officially documented other than the 'Friend' invite type, invites that point directly to a user are supported.
  • This raises the issue of invites not having either a guild(_id) or a channel(_id) associated with them, as the Invite class hints that guild, guild_id, and channel can be None but not channel_id. The channel field in an Invite response object is described as being nullable
  • These friend-specific invites look like this (note the null channel and type: 2)

    {
      "code": "<invitecode>",
      "inviter": { < inviter user object > },
      "channel": null,
      "type": 2,
      "uses": 0,
      "max_uses": 5,
      "max_age": 604800,
      "created_at": "2025-03-19T11:40:31.885200+00:00",
      "expires_at": "2025-03-26T11:40:31+00:00"
    }
    

    
  • The max_uses is always set to 5, and max_age is always 7 days/expires_at is always created_at + 7 days
• guild_scheduled_event(_id) is also listed as a possible (nullable) field on an Invite object, but it's missing from invites.Invite and should be added