Wrong curve when using Manim Ellipse

### Describe the bug
**The curve of the ellipse is too small!**
The curve must interpolate the four vertices A,B,C,D but it doesn't!

**Code**:
```
from manim import *
class EllipseExample(Scene):
def construct(self):
w, h = 3.0, 2.0
ellipse_1 = Ellipse(width=w*2, height=h*2, color=BLUE_B)
self.add(ellipse_1)
A, B, C, D = Dot([-w,0,0]), Dot([w,0,0]), Dot([0,-h,0]), Dot([0,h,0])
self.add(A, B, C, D)
self.add(Line([-w*1.1, 0, 0], [w*1.1, 0, 0], color=GRAY))
self.add(Line([0, -h*1.1, 0], [0, h*1.1, 0], color=GRAY))
```

**Wrong display or Error traceback**:

### Additional context
Apparently **the internally used points are wrong**, see get_shader_data().

此問題出在 Ellipse 類別；先檢查 get_shader_data() 方法，查看頂點如何計算。將計算出的點與預期頂點 (-w,0), (w,0), (0,-h), (0,h) 比較。執行提供的程式碼以重現視覺差異，然後調整頂點產生或插值邏輯。檢查 ellipse 渲染的測試檔案，以確保修正不會破壞現有測試。

由索引模型根據 Issue 內容生成。