gh-36089: `sage.geometry.polyhedron`: fix doctest error due to modularization
    
On MacOS with sagemath 10.1.rc0, I have the following doctest error in
`src/sage/geometry/polyhedron/base_ZZ.py`

```
sage -t --long --warn-long 18.5 --random-
seed=240228246560107174999702016603267109757
src/sage/geometry/polyhedron/base_ZZ.py
**********************************************************************
File "src/sage/geometry/polyhedron/base_ZZ.py", line 419, in
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?
Failed example:
    hypercube(3).ehrhart_polynomial(engine='normaliz')
Exception raised:
    Traceback (most recent call last):
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 709,
in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 1144,
in compile_and_execute
        exec(compiled, globs)
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[9]>", line 1, in
<module>
        hypercube(Integer(3)).ehrhart_polynomial(engine='normaliz')
        ^^^^^^^^^^^^^^^^^^^^^
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[8]>", line 2, in
hypercube
        return Polyhedron(vertices=list(product([Integer(0),Integer(1)],
repeat=d)),backend='normaliz')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: 'sage.rings.integer.Integer' object is not iterable
**********************************************************************
File "src/sage/geometry/polyhedron/base_ZZ.py", line 421, in
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?
Failed example:
    hypercube(4).ehrhart_polynomial(engine='normaliz')
Exception raised:
    Traceback (most recent call last):
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 709,
in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 1144,
in compile_and_execute
        exec(compiled, globs)
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[10]>", line 1, in
<module>
        hypercube(Integer(4)).ehrhart_polynomial(engine='normaliz')
        ^^^^^^^^^^^^^^^^^^^^^
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[8]>", line 2, in
hypercube
        return Polyhedron(vertices=list(product([Integer(0),Integer(1)],
repeat=d)),backend='normaliz')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: 'sage.rings.integer.Integer' object is not iterable
**********************************************************************
File "src/sage/geometry/polyhedron/base_ZZ.py", line 423, in
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?
Failed example:
    hypercube(5).ehrhart_polynomial(engine='normaliz')
Exception raised:
    Traceback (most recent call last):
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 709,
in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 1144,
in compile_and_execute
        exec(compiled, globs)
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[11]>", line 1, in
<module>
        hypercube(Integer(5)).ehrhart_polynomial(engine='normaliz')
        ^^^^^^^^^^^^^^^^^^^^^
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[8]>", line 2, in
hypercube
        return Polyhedron(vertices=list(product([Integer(0),Integer(1)],
repeat=d)),backend='normaliz')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: 'sage.rings.integer.Integer' object is not iterable
**********************************************************************
File "src/sage/geometry/polyhedron/base_ZZ.py", line 425, in
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?
Failed example:
    hypercube(6).ehrhart_polynomial(engine='normaliz')
Exception raised:
    Traceback (most recent call last):
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 709,
in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/Users/dcoudert/sage/src/sage/doctest/forker.py", line 1144,
in compile_and_execute
        exec(compiled, globs)
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[12]>", line 1, in
<module>
        hypercube(Integer(6)).ehrhart_polynomial(engine='normaliz')
        ^^^^^^^^^^^^^^^^^^^^^
      File "<doctest
sage.geometry.polyhedron.base_ZZ.Polyhedron_ZZ.?[8]>", line 2, in
hypercube
        return Polyhedron(vertices=list(product([Integer(0),Integer(1)],
repeat=d)),backend='normaliz')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    TypeError: 'sage.rings.integer.Integer' object is not iterable
```

This is caused by the `from itertools import product` in a block
starting with `# optional - latte_int`. Apparently I don't have
`latte_int` installed, and so this import is not done when starting the
block with `pynormaliz` (I have it). So the fix is trivial.

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URL: #36089
Reported by: David Coudert
Reviewer(s): Matthias Köppe

Author: Release Manager

src/sage/geometry/polyhedron/base_ZZ.py

@@ -414,6 +414,7 @@ def ehrhart_polynomial(self, engine=None, variable='t', verbose=False, dual=None
             t^6 + 6*t^5 + 15*t^4 + 20*t^3 + 15*t^2 + 6*t + 1
 
             sage: # optional - pynormaliz
+            sage: from itertools import product
             sage: def hypercube(d):
             ....:     return Polyhedron(vertices=list(product([0,1],repeat=d)),backend='normaliz')
             sage: hypercube(3).ehrhart_polynomial(engine='normaliz')