FDK for V-offset missing

I am trying to do CBCT reconstruction. There is a detector offset in the Z-axis, namely ` geo.offDetector = [0; -120]; % Offset of Detector (mm) ` which leads to insufficient data on both sides of the Z-axis and obvious artifacts. Is there any good way？ #151 @dyycy

## Actual Behavior


Pocs-tv algorithm is used by me to increase the number of reconstructed image layers, but Now I try to use FDK algorithm to do it. There are x-FDK, HD-FDK, V-FDK and other algorithms maybe improve image.

Start by reading issue #151 and the discussion in this issue, then inspect TIGRE's existing FDK, HD-FDK, and V-FDK support. Determine whether detector offsets in the Z-axis are supported and what behavior is expected; the work is done when the requested V-offset reconstruction path is implemented or its lack of support is clearly resolved.

Written by the indexing model from the issue text.