SphereTransform: center coords are not relative

The arguments to `SphereTransform` are called `relative_center_{xyz}`, but the call to `ReslicePolar.reslice` is performing translation in pixel units, without any normalization:

https://github.com/clij/clij2/blob/5c716fb414c57a42617490e8135bd07d3c4044d9/src/main/java/net/haesleinhuepf/clij2/plugins/SphereTransform.java#L54-L59

https://github.com/clij/clij2/blob/5c716fb414c57a42617490e8135bd07d3c4044d9/src/main/java/net/haesleinhuepf/clij2/plugins/ReslicePolar.java#L75-L76

I'd suggest to either rename the arguments to `center_{xyz}`, or to (re-)introduce some normalization to image dimensions before that call.

Start with SphereTransform.java lines 54-59 and ReslicePolar.java lines 75-76, then trace how relative_center_{xyz} reaches ReslicePolar.reslice. Determine whether the intended fix is renaming the arguments or restoring normalization; done means the argument names and coordinate units consistently describe the resulting transform.

Written by the indexing model from the issue text.