fix: bunch of bugs related to text highlighting (#59)

- Fixes highlighting not clearing when you click somewhere else
- Fixes autoscroll not working when you highlight and drag up or down
- Fixes copy/paste related to highlighting

Author: sreya

lib/renderer.ts

@@ -308,15 +308,15 @@ export class CanvasRenderer {
       }
     }
 
-    // Always mark previous selection rows for redraw (to clear old overlay)
+    // Always mark dirty selection rows for redraw (to clear old overlay)
     if (this.selectionManager) {
-      const prevCoords = this.selectionManager.getPreviousSelectionCoords();
-      if (prevCoords) {
-        for (let row = prevCoords.startRow; row <= prevCoords.endRow; row++) {
+      const dirtyRows = this.selectionManager.getDirtySelectionRows();
+      if (dirtyRows.size > 0) {
+        for (const row of dirtyRows) {
           selectionRows.add(row);
         }
-        // Clear the previous selection tracking after marking for redraw
-        this.selectionManager.clearPreviousSelection();
+        // Clear the dirty rows tracking after marking for redraw
+        this.selectionManager.clearDirtySelectionRows();
       }
     }