CuasRTUtils: new filterConv5dROI(data, roi, athresh, rthresh)
  For each (pixel, velocity) point, finds max M over the ±1 neighbourhood
  in both pixel space (3×3) and velocity space (3×3 in vx/vy).
  Zeroes the point if M >= athresh AND val < rthresh*M (sidelobe suppression).
  Passes through unchanged when M < athresh (weak-signal linear regime).
  Uses indx_center_3d3 / indx_margins_3d3 for bit-reversed multithreaded
  pixel iteration; returns a new filtered array.

CuasDetectRT: apply filterConv5dROI() to dpixels_5d_roi_pyramid[level][n5d]
  after convolve3d(), controlled by curt_vel_thresh_en / curt_vel_athresh /
  curt_vel_rthresh, at level-0 and all pyramid levels.
Co-authored-by: Claude <claude@elphel.com>