[Feature Request] ---@final to mark class method as non-overridable

In languages like Java, you have the keyword final to indicate that a function should NOT be overridden. There doesn't seem to be any annotation like that yet. It should give a warning (or error?) if you try to override the function. Additionally, completion for function MyClass: could avoid suggesting anything with @final? You'd still be able to call it anywhere, just not override it if its now final.

(Maybe @final could also work on variables? Pretty much working the same way, just "don't override/set this but still be able to read it")

(Unrelated but I was thinking about ---@override to mark something as "you should override this and not call this" but it wouldn't be able to warn since your internal code needs to call it, so I'm not sure. Might just be good to have anyway, not as a warning but a tooltip thing.)

未指定原始檔、測試或進入點。首先釐清 @final 是套用於方法、變數，還是兩者，以及違規會產生警告還是錯誤；然後檢查語言伺服器的註解、覆寫檢查和補全行為。當選定的語意獲得一致實作，並由診斷或補全測試涵蓋時，即表示完成。