docs: process cell magics (#4462)

Handle a small thing that can be fairly confusing to new python users.

Before:


![image](https://github.com/user-attachments/assets/39011f0c-0a7e-4f32-94d7-a40f0b14f2ab)


After:


![image](https://github.com/user-attachments/assets/16aa4429-eb4e-44b5-8714-29279d93c7ea)

docs/tests/unit_tests/test_notebook_conversion.py

@@ -1,8 +1,13 @@
+import os
+import tempfile
+
+import nbformat
 import pytest
 
 from _scripts.notebook_convert import (
     _convert_links_in_markdown,
     _has_output,
+    convert_notebook,
 )
 
 
@@ -32,3 +37,41 @@ def test_has_output() -> None:
 def test_link_conversion(source: str, expected: str) -> None:
     """Test logic to convert links in markdown cells."""
     assert _convert_links_in_markdown(source) == expected
+
+
+EXPECTED_OUTPUT = """\
+```shell
+pip install -U langgraph
+```
+
+
+```python
+print('Hello')
+```\
+
+"""
+
+
+def test_converting_cell_magic() -> None:
+    """Test converting cell magic to code blocks."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        nb_path = os.path.join(tmpdir, "test_notebook.ipynb")
+
+        # Create a minimal notebook object
+        nb = nbformat.v4.new_notebook()
+        nb.cells = [
+            nbformat.v4.new_code_cell(
+                "%%capture --no-stderr\n"
+                "%pip install -U langgraph"
+            ),
+            nbformat.v4.new_code_cell("print('Hello')"),
+        ]
+        nb.metadata["language_info"] = {"name": "python"}
+
+        # Write to file
+        with open(nb_path, "w", encoding="utf-8") as f:
+            nbformat.write(nb, f)
+
+        # Run the conversion
+        converted = convert_notebook(nb_path)
+        assert converted == EXPECTED_OUTPUT