Incomplete Fix for CVE-2026-1669: HDF5 External Storage File Disclosure in Legacy H5 Loading

Description Keras 3 patched CVE-2026-1669 HDF5 External Storage File Disclosure in the new .keras and .weights.h5 loading paths by adding verifydataset to check for dataset.external in H5IOStore. However, the legacy .h5 loading path keras/src/legacy/saving/legacyh5format.py was not patched. This...