SinglefileData: Add mode keyword to get_content

This allows a user to retrieve the content in bytes. Currently, a user
is forced to use the more elaborate form:

    with singlefile.open(mode='rb') as handle:
        content = handle.read()

or go directly through the repository interface which is a bit hidden
and requires to redundantly specify the filename:

    content = singlefile.base.repository.get_object_content(
	singlefile.filename,
	mode='rb'
    )

these variants can now be simplified to:

    content = singlefile.get_content('rb')

aiida/orm/nodes/data/singlefile.py

@@ -92,12 +92,13 @@ def open(self, path: str | None = None, mode: t.Literal['r', 'rb'] = 'r') -> t.I
         with self.base.repository.open(path, mode=mode) as handle:
             yield handle
 
-    def get_content(self) -> str:
+    def get_content(self, mode: str = 'r') -> str | bytes:
         """Return the content of the single file stored for this data node.
 
-        :return: the content of the file as a string
+        :param mode: the mode with which to open the file handle (default: read mode)
+        :return: the content of the file as a string or bytes, depending on ``mode``.
         """
-        with self.open(mode='r') as handle:  # type: ignore[call-overload]
+        with self.open(mode=mode) as handle:  # type: ignore[call-overload]
             return handle.read()
 
     def set_file(self, file: str | t.IO, filename: str | pathlib.Path | None = None) -> None:

tests/orm/nodes/data/test_singlefile.py

@@ -198,3 +198,11 @@ def test_from_string():
     node = SinglefileData.from_string(content, filename).store()
     assert node.get_content() == content
     assert node.filename == filename
+
+
+def test_get_content():
+    """Test the :meth:`aiida.orm.nodes.data.singlefile.SinglefileData.get_content` method."""
+    content = b'some\ncontent'
+    node = SinglefileData.from_string(content.decode('utf-8')).store()
+    assert node.get_content() == content.decode('utf-8')
+    assert node.get_content('rb') == content