Fix Kabsch algorithm (rigid alignment)

[VincentBt]

Hi! Thank you for this piece of work. I noticed a mistake in your rotation matrix computation (part of the Kabsch algorithm for alignment) here:

# Rotation matrix
R = V.mm(U.T)

should be replaced with

# Rotation matrix
R = V.mm(U.T)
# Ensure R is a proper rotation matrix
if torch.det(R) < 0:  # reflection
    V[:, -1] *= -1  # flip the sign of the last column of V
    R = V.mm(U.T)

See this link for justification

[shenoynikhil]

Thanks for looking into this and for the quick PR.