[Code scan] Restore vendored xitorch sampled quadrature imports

[njzjz]

This issue comes from a Codex global repository scan.

Problem

The vendored sampled quadrature module imports the vendored package root and subclasses xt.EditableModule:

dftio/dftio/dep/_xitorch/_impls/integrate/samples_quad.py

Lines 1 to 11 in c9d128f

	import torch
	import dftio.dep._xitorch as xt
	from abc import abstractmethod
	from dftio.dep._xitorch._impls.interpolate.interp_1d import _get_spline_mat_inv
	"""
	This file contains the cumulative sum quadrature functions.
	The functions are usually used in solve_poisson method in grid objects.
	"""
	class BaseSQuad(xt.EditableModule):

But dftio/dep/_xitorch/__init__.py is empty, so EditableModule is not exported there. Importing the module raises:

AttributeError: module 'dftio.dep._xitorch' has no attribute 'EditableModule'

Suggested fix

Either import EditableModule directly from dftio.dep._xitorch._core.editable_module, or re-export it from the vendored package root.