Celestial meridian labels incorrect for eck4 projection

还没有人认领这个 Issue。

I am testing the following eck4 meridian labeling example:

```
def label_bug(celestial=True, lon_0=65):
m = Basemap(projection='eck4', lon_0=lon_0, resolution=None, celestial=celestial)
m.drawmeridians([lon_0, lon_0 + 60], labels=[0,0,1,0], labelstyle='+/-')
m.drawmapboundary()
```

With normal coordinates, the labels appear where I expect them:

```
label_bug(celestial=False)
```

When celestial is True, the meridians are correctly flipped, but the labels no longer match their positions:

```
label_bug(celestial=True)
```

If anyone knows a workaround until this is fixed, please let me know. Thanks!

从提供的 label_bug 复现和 Basemap.drawmeridians 开始，针对 eck4 投影比较 celestial=False 和 celestial=True。跟踪子午线位置和标签是如何转换的，然后使用该示例验证在两种情况下标签都与显示的子午线匹配。

由索引模型根据 Issue 内容生成。