gh-155452: Prevent recursion crash in dir() - #155453

gh-155452: Prevent recursion crash in dir() when __bases__ is cyclic.

Summary

dir() could cause a native stack overflow when an object's __class__
provided a cyclic __bases__ attribute.

merge_class_dict() recursively traverses __bases__ without a recursion
guard. This change protects that recursion with _Py_EnterRecursiveCall()
and _Py_LeaveRecursiveCall(), matching the existing protection in
abstract_issubclass().

Changes

• Add the required pycore_ceval.h include.
• Guard recursive __bases__ traversal in merge_class_dict().
• Add a regression test using a one-node cyclic __bases__ graph.
• Add a NEWS entry.

Testing

Before the fix, the reproducer resulted in:

Segmentation fault
rc=139

After the fix, it raises:

RecursionError: Stack overflow (used 8120 kB) in __bases__

Targeted regression test:

./python -m test test_builtin -m test_dir
== Tests result: SUCCESS ==
1 test OK.

Closes issue gh-155452