grade_answe 测试有纰漏

我在使用 `grade.grade_answer` 函数比对 `0.5 + \\frac{\\pi}{8}` 和 `\\pi \\div 8 + 1 \\div 2` 并不被判断为相等的表达式

使用的版本应该是 mathrule 0.1.0

我跟踪到函数中，发现执行到的分支是
```
else:
for ground_truth_elem, given_elem in zip(ground_truth_elems, given_elems):
if _is_frac(ground_truth_elem) and _is_frac(given_elem):
# if fractions aren't reduced, then shouldn't be marked as correct
# so, we don't want to allow sympy.simplify in this case
is_correct = ground_truth_elem == given_elem
elif _str_is_int(ground_truth_elem) != _str_is_int(given_elem):
# if the ground truth answer is an integer, we require the given answer to be a strict match (no sympy.simplify)
is_correct = False
else:
# ！ 执行到这里
is_correct = are_equal_under_sympy(ground_truth_elem, given_elem)
if not is_correct:
break

```

也就是 smpy 没有将这两个表达式当成一样的，请问有没有什么调整的方法？