Attack Cooldown Remover

Some improvements (thanks, 4drian3d):

• Replaced static access to the server with a class access from the plugin instance,
• Replaced the use of System.out.println with the plugin logger. This avoids warnings in Paper servers,
• Upgraded the Java compatible version to Java 17 and use the new pattern matching,
• Now it avoids throwing an exception through the "assert" in case the AttributeInstance is null, now simply use the variable if it is not null.