fix: change calculation from fy to match square pixel assumption

[ahamboeck]

Align camera_info intrinsics with depth → point cloud (square pixels assumption)

Summary

This PR updates the fy calculation in camera_info_utils.py so that it matches the depth → point cloud implementation (OgnIsaacConvertDepthToPointCloud.cpp).

Previously, camera_info_utils.py calculated fy using the vertical aperture:

fy = height * focalLength / verticalAperture

But in depth → point cloud, fy was already implemented as:

// We assume that we have square pixels so fy = height * focalLength / (horizontalAperture * (height / width))
fx = width * focalLength / horizontalAperture;
fy = height * focalLength / (horizontalAperture * (height / width));
cx = width * 0.5f;
cy = height * 0.5f;

This simplifies to:

fy = width * focalLength / horizontalAperture

which makes fy the same as fx.

With this PR, camera_info_utils.py now uses the same formula as the depth → point cloud path, enforcing the square pixel assumption consistently.

Why

• Avoids mismatched intrinsics between camera_info and depth_pcl.
• Makes the assumption of square pixels explicit (sensor aspect ratio must match resolution).
• Keeps behavior consistent across both camera_info and point cloud generation.

Recommendation

• Update the documentation to clearly state that square pixels must be used.
• Clarify that both fx and fy are derived from the horizontal aperture under this assumption.

References

• Related issue: #199
• Forum discussion: https://forums.developer.nvidia.com/t/bug-ros2-omnigraph-camera-info-camera-intrisics/344939/3
• Depth → point cloud code: OgnIsaacConvertDepthToPointCloud.cpp#L60
• Camera info utils: camera_info_utils.py#L87