fix(markdown): handle nested lists (#910)

Signed-off-by: Panos Vagenas <35837085+vagenas@users.noreply.github.com>

tests/data/groundtruth/docling_v2/nested.md.md

@@ -0,0 +1,31 @@
+# Nesting
+
+A list featuring nesting:
+
+- abc
+    - abc123
+        - abc1234
+            - abc12345
+                - a.
+                - b.
+        - abcd1234：
+            - abcd12345：
+                - a.
+                - b.
+- def：
+    - def1234：
+        - def12345。
+- after one empty line
+    - foo
+- afer two empty lines
+    - bar
+
+- changing symbol
+
+A nested HTML list:
+
+- First item
+- Second item with subitems:
+    - Subitem 1
+    - Subitem 2
+- Last list item