[Feature] Nickname check duplication

[MsEDok]

Proposed Feature Description:

Nickname command check for name already in use or duplicate.

Proposed Feature Functionality:

Username: MsEDok
When setting the nickname to MrEDok while Player MrEDok online/offline should not be possible.
When a player is offline with nickname "test" i should not be able to have the same nickname as test

currently when player 1 set their nickname to test and log out or server restart
player 2 can join and set their nickname to test

now when both of them are online we will have "2" player with nickname test which make it very confusing to know who is who.

Functionality should be that

• when a player try to set their nickname
• plugin check for online player nickname
• offline nickname
• and the username of the offline
  so they cannot impersonate (i know plugin can add ~to the name but it can still be confusing)

I also notice that if a player didn't do anything on the server their data doesn't get saved to the database it only happen when a player change their nickname or ignore someone then it will save.

if the data always get saved to database regardless of data change or not it should prob be easier to also check what their username, nickname is neing set to.