MSBIndex operation for Sqrt

[jvmncs]

The current MSB operation for replicated tensors essentially checks the condition x > 0, but for Sqrt we require an MSBIndex operation that accepts a replicated fixedpoint of total precision k and returns a vector of length k of replicated bits, where the bit at the position of the MSB is 1 and all other vector elements are 0. This has the same semantics as the MSB operation defined for fixedpoints in the Scale-Mamba documentation .