🐛 Restore ArrayData array serialization helpers (#7480)

Restore the public `ArrayData.save_arrays()` and
`ArrayData.load_arrays()` helpers.

These utilities are self-contained compatibility helpers for
serializing numpy arrays to base64-encoded `.npy` payloads and
loading them back. Add regression coverage for the roundtrip.

Author: agoscinski

src/aiida/orm/nodes/data/array/array.py

@@ -10,6 +10,8 @@
 
 from __future__ import annotations
 
+import base64
+import io
 from collections.abc import Iterable, Iterator, Sequence
 from typing import Any, BinaryIO
 
@@ -116,6 +118,55 @@ def __init__(self, arrays: Iterable | dict[str, Iterable] | None = None, **kwarg
         for key, value in arrays.items():
             self.set_array(key, np.asarray(value))
 
+    @staticmethod
+    def save_arrays(arrays: dict[str, np.ndarray]) -> dict[str, bytes]:
+        """Serialize arrays to base64-encoded ``.npy`` payloads.
+
+        :param arrays: Mapping of array names to numpy arrays.
+        :return: Mapping of array names to base64-encoded bytes.
+        """
+        from aiida.common.warnings import warn_deprecation
+
+        warn_deprecation(
+            '`ArrayData.save_arrays` is deprecated. Use `numpy.save` with `io.BytesIO` directly instead.',
+            version=3,
+            stacklevel=2,
+        )
+
+        results = {}
+
+        for key, array in arrays.items():
+            stream = io.BytesIO()
+            np.save(stream, array, allow_pickle=False)
+            stream.seek(0)
+            results[key] = base64.encodebytes(stream.read())
+
+        return results
+
+    @staticmethod
+    def load_arrays(arrays: dict[str, bytes]) -> dict[str, np.ndarray]:
+        """Deserialize arrays from base64-encoded ``.npy`` payloads.
+
+        :param arrays: Mapping of array names to base64-encoded bytes.
+        :return: Mapping of array names to numpy arrays.
+        """
+        from aiida.common.warnings import warn_deprecation
+
+        warn_deprecation(
+            '`ArrayData.load_arrays` is deprecated. Use `numpy.load` with `io.BytesIO` directly instead.',
+            version=3,
+            stacklevel=2,
+        )
+
+        results = {}
+
+        for key, encoded in arrays.items():
+            stream = io.BytesIO(base64.decodebytes(encoded))
+            stream.seek(0)
+            results[key] = np.load(stream, allow_pickle=False)
+
+        return results
+
     @property
     def arrays(self) -> dict[str, np.ndarray]:
         return {name: self.get_array(name) for name in self.get_arraynames()}

tests/orm/nodes/data/test_array.py

@@ -11,6 +11,7 @@
 import numpy
 import pytest
 
+from aiida.common.warnings import AiidaDeprecationWarning
 from aiida.orm import ArrayData, load_node
 
 
@@ -61,3 +62,22 @@ def test_get_array():
 
     node = ArrayData(numpy.array([1, 2]))
     assert (node.get_array() == numpy.array([1, 2])).all()
+
+
+def test_save_and_load_arrays():
+    """Test :meth:`aiida.orm.ArrayData.save_arrays` and ``load_arrays``."""
+    arrays = {
+        'a': numpy.array([1, 2, 3]),
+        'b': numpy.array([[1.0, 2.0], [3.0, 4.0]]),
+    }
+
+    with pytest.warns(AiidaDeprecationWarning, match='ArrayData.save_arrays'):
+        serialized = ArrayData.save_arrays(arrays)
+    assert set(serialized) == {'a', 'b'}
+    assert all(isinstance(value, bytes) for value in serialized.values())
+
+    with pytest.warns(AiidaDeprecationWarning, match='ArrayData.load_arrays'):
+        deserialized = ArrayData.load_arrays(serialized)
+    assert set(deserialized) == {'a', 'b'}
+    assert numpy.array_equal(deserialized['a'], arrays['a'])
+    assert numpy.array_equal(deserialized['b'], arrays['b'])