gh-39468: Fix documentation of integral_points
    
Fixes #39395

Replacement for #39414

Check https://doc-pr-39468--
sagemath.netlify.app/html/en/reference/discrete_geometry/ and
https://doc-pr-39468--sagemath.netlify.app/html/en/reference/discrete_ge
ometry/sage/geometry/integral_points to see it is fixed.

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preview.

### ⌛ Dependencies

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URL: #39468
Reported by: user202729
Reviewer(s):

Author: Release Manager

src/sage/geometry/integral_points.py

@@ -1,3 +1,7 @@
+r"""
+Cython helper methods to compute integral points in polyhedra
+"""
+
 try:
     from .integral_points_integer_dense import (
         parallelotope_points,
@@ -22,3 +26,9 @@
         Inequality_int,
         InequalityCollection,
     )
+
+
+# __all__ is needed to generate Sphinx documentation
+__all__ = ['InequalityCollection', 'Inequality_generic', 'Inequality_int',
+           'loop_over_parallelotope_points', 'parallelotope_points', 'print_cache',
+           'ray_matrix_normal_form', 'rectangular_box_points', 'simplex_points']