[BUG] Axis lengths of confidence ellipse are computed wrong

### Description of the bug

Should be this
![image](https://github.com/vortexntnu/vortex-vkf/assets/64218254/0850bccf-9a77-46c1-98ab-ffd94811f4fd)

Currently the scale is inside the square root ([here](https://github.com/vortexntnu/vortex-vkf/blob/main/vortex-filtering/src/utils/ellipse.cpp))


### Steps To Reproduce

_No response_

### Additional Information

_No response_