fix(browser): reset TimeBasedDebouncer state on dispose

dispose() cleared the pending timeout but left _refreshTimeoutID and
_additionalRefreshRequested set. After dispose, a stale timeout id or
trailing-refresh flag could confuse a new instance or tests. Match
RenderDebouncer by clearing the timeout id and reset the trailing flag.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/browser/TimeBasedDebouncer.ts

@@ -31,7 +31,9 @@ export class TimeBasedDebouncer implements IRenderDebouncer {
   public dispose(): void {
     if (this._refreshTimeoutID) {
       clearTimeout(this._refreshTimeoutID);
+      this._refreshTimeoutID = undefined;
     }
+    this._additionalRefreshRequested = false;
   }
 
   public refresh(rowStart: number | undefined, rowEnd: number | undefined, rowCount: number): void {