Add convolve3d() (kernel5d) at level-0 before the temporal pyramid loop
and at each pyramid level nlev+1 inside the loop, mirroring the existing
3D3 coarse-velocity pattern. Output saved as CONV5D hyperstack when
debugLevel > -4. Add getNumHist() getter to CuasRTUtils.
Co-authored-by: Claude <claude@elphel.com>