NeXus: record sample position in real motor positions

Sample position appear to be recorded in "virtual" motor position, rather than actual SmarGon motor positions. See e.g. the output of `h5ls` for the following two datasets - the first is at `omega=0` which has `z=0` (this should be constant, but probably non-zero), and the second dataset at `omega=0` also has `z=0`, where in fact `y` should be fixed (again at a non-zero value), and `x` and `z` should be moving:
```
$ h5ls -rd /dls/i03/data/2022/cm31105-2/xraycentring/manual/xrc_197_master.h5/entry/sample/transformations/
$ h5ls -rd /dls/i03/data/2022/cm31105-2/xraycentring/manual/xrc_198_master.h5/entry/sample/transformations/
```
I note that there are also 420 positions recorded, when there should only be 380 from the grid size that was collected - this looks like there is an extra row and column recorded than was actually the case.

Another issue is that omega is reported as zero in both NeXus files.