after amending a few more bugs, it seems that line metadata and index metadata are handled correctly. At least for svelte dataset; worth checking others as well

tests/compare_to_rope.sml

@@ -16,12 +16,16 @@ struct
            val gapBuffer =
              if delNum > 0 then LineGap.delete (pos, delNum, gapBuffer)
              else gapBuffer
+
+           val _ = LineGap.verifyIndex gapBuffer
+           val _ = LineGap.verifyLines gapBuffer
+
            val gapBuffer =
              if strSize > 0 then LineGap.insert (pos, insStr, gapBuffer)
              else gapBuffer
 
-          val _ = LineGap.verifyIndex gapBuffer
-          val _ = LineGap.verifyLines gapBuffer
+           val _ = LineGap.verifyIndex gapBuffer
+           val _ = LineGap.verifyLines gapBuffer
 
            val ropeString = TinyRope.toString rope
            val gapBufferString = LineGap.toString gapBuffer