core[patch]: fixed circular dependency with json schema (#18657)

**Description:** Circular dependencies when parsing references leading
to `RecursionError: maximum recursion depth exceeded` issue. This PR
address the issue by handling previously seen refs as in any typical DFS
to avoid infinite depths.

**Issue:** https://github.com/langchain-ai/langchain/issues/12163

 **Twitter handle:** https://twitter.com/theBhulawat 


- [x] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>
Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

libs/core/tests/unit_tests/utils/test_json_schema.py

@@ -181,3 +181,54 @@ def test_dereference_refs_integer_ref() -> None:
     }
     actual = dereference_refs(schema)
     assert actual == expected
+
+
+def test_dereference_refs_cyclical_refs() -> None:
+    schema = {
+        "type": "object",
+        "properties": {
+            "user": {"$ref": "#/$defs/user"},
+            "customer": {"$ref": "#/$defs/user"},
+        },
+        "$defs": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {"type": "array", "items": {"$ref": "#/$defs/user"}}
+                },
+            }
+        },
+    }
+    expected = {
+        "type": "object",
+        "properties": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {
+                        "type": "array",
+                        "items": {},  # Recursion is broken here
+                    }
+                },
+            },
+            "customer": {
+                "type": "object",
+                "properties": {
+                    "friends": {
+                        "type": "array",
+                        "items": {},  # Recursion is broken here
+                    }
+                },
+            },
+        },
+        "$defs": {
+            "user": {
+                "type": "object",
+                "properties": {
+                    "friends": {"type": "array", "items": {"$ref": "#/$defs/user"}}
+                },
+            }
+        },
+    }
+    actual = dereference_refs(schema)
+    assert actual == expected