Get data file buffers from python API

Summary:
#14133

Retrieve tensor data as a buffer (like executorch_program.buffer), so it can be used in pybindings, see D82046648

Differential Revision: D82061884

Author: lucylq

exir/program/_program.py

@@ -22,6 +22,7 @@
 )
 from executorch.exir._serialize._serialize import serialize_for_executorch
 from executorch.exir._serialize.data_serializer import DataSerializer
+from executorch.exir._warnings import experimental
 from executorch.exir.backend.backend_api import (
     MethodProgramsPartitionerSpec,
     to_backend,
@@ -626,6 +627,24 @@ def buffer(self) -> bytes:
             self._buffer = bytes(self._get_pte_data())
         return self._buffer
 
+    @property
+    @experimental("This API is experimental and subject to change without notice.")
+    def data_files(self) -> Dict[str, bytes]:
+        """Returns the data files as a dictionary of filename to byte data.
+
+        Returns:
+            Dict[str, bytes]: Dictionary mapping data filenames (e.g., .ptd files) to
+                their serialized byte content.
+            Returns empty dict if no data files are available.
+        """
+        if self._pte_data is None:
+            self._get_pte_data()  # This populates _tensor_data
+
+        if self._tensor_data is None:
+            return {}
+
+        return {filename: bytes(cord) for filename, cord in self._tensor_data.items()}
+
     @property
     def program(self) -> Program:
         return self._get_emitter_output().program