Translate code comment to Chinese: "Calculate speed gain" → "计算加速比"

Agent-Logs-Url: https://github.com/QuantEcon/lecture-python-programming.zh-cn/sessions/2637b9b4-16b3-474d-9729-3ea2aed221c0

Co-authored-by: HumphreyYang <39026988+HumphreyYang@users.noreply.github.com>

Author: Copilot

lectures/numba.md

@@ -162,7 +162,7 @@ time3 = timer3.elapsed
 ```
 
 ```{code-cell} ipython3
-time1 / time3  # Calculate speed gain
+time1 / time3  # 计算加速比
 ```
 
 ### 工作原理与适用时机