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

tests/data/md/nested.md

@@ -0,0 +1,66 @@
+# 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:
+
+<ul>
+    <li>First item</li>
+    <li>Second item with subitems:
+        <ul>
+            <li>Subitem 1</li>
+            <li>Subitem 2</li>
+        </ul>
+    </li>
+    <li>Last list item</li>
+</ul>
+
+<!--
+Table nesting apparently not yet suported by HTML backend:
+
+<table>
+  <tr>
+    <td>Cell</td>
+    <td>Nested Table
+      <table>
+        <tr>
+          <td>Cell 1</td>
+		  <>
+        </tr>
+        <tr>
+          <td>Cell 2</td>
+        </tr>
+        <tr>
+          <td>Cell 3</td>
+        </tr>
+        <tr>
+          <td>Cell 4</td>
+        </tr>
+      </table>
+    </td>
+  </tr>
+  <tr><td>additional row</td></tr>
+</table>
+-->