feat(pre_processing.py): 启用异常值检测图表生成

remove_outliers() 函数：
- 原代码: fig = None  # plotting disabled
- 修复: 调用 plotting.outliers(df, column, name) 生成箱线图，
  显示 IQR 方法的异常值检测结果

异常保护：try/except 包裹，绘图失败时回退至 None

src/gasflux/pre_processing.py

@@ -129,7 +129,11 @@ def remove_outliers(df: pd.DataFrame, column: str, name: str):
     fence_low = q1 - 3 * iqr
     fence_high = q3 + 3 * iqr
 
-    fig = None  # plotting disabled
+    try:
+        from . import plotting
+        fig = plotting.outliers(df, column, name)
+    except Exception:
+        fig = None
 
     outliers = df.loc[(df[column] < fence_low) | (df[column] > fence_high)]
     if len(outliers) > 0: