feat: add mathjax renderer

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[YangFong]

测试数据：

# 测试

前面一半

$$
\underbrace{| Z - \text{sg}[\tilde{Z}] |2^2}
$$

后面一半

$$
{\mathcal{L}{commit}}
$$

完整

$$
\underbrace{| Z - \text{sg}[\tilde{Z}] |2^2}{\mathcal{L}{commit}}
$$

[yanglbme]

测试用例：

1. 引用内加公式：

> 这段代码时间复杂度 $O(n^2)$，空间复杂度 $O(n)$。

2. 复杂公式：

$$
\mathcal{L}_{VQ} = \underbrace{\mathcal{L}_{CE}(X, \hat{X})}_{\mathcal{L}_{rec}} + \underbrace{\| \text{sg}[Z] - \tilde{Z} \|_2^2}_{\mathcal{L}_{code}} + \beta \underbrace{\| Z - \text{sg}[\tilde{Z}] \|_2^2}_{\mathcal{L}_{commit}}, \tag{4}
$$

3. 行内公式，前后不加空格：

这段代码时间复杂度$O(n^2)$，空间复杂度$O(n)$。

[yanglbme]

$$
f[i][h]=
\begin{cases}
\max(f[i][h], f[j][h] + 1234343243444554545), & \textit{if } nums[i] = nums[j], \\
\max(f[i][h], f[j][h - 1] + 1), & \textit{if } h > 0.
\end{cases}
$$

[yanglbme]

376 #384