fix: cross-product produces left-handed coordinate frame

[Mr-Neutr0n]

Bug

In average_poses() in dataLoader/llff.py, the cross product operands for computing the camera coordinate frame axes are in the wrong order, producing a left-handed frame instead of the standard right-handed frame.

The comments correctly describe the intended computation:

• Step 4: "Compute x' = y' cross product z"
• Step 5: "Compute the y axis: z cross product x"

But the code had the operands swapped:

• np.cross(z, y_) instead of np.cross(y_, z)
• np.cross(x, z) instead of np.cross(z, x)

Fix

Swapped the cross product operands to match the documented algorithm and produce the correct right-handed coordinate system.