Add an inplace option for transformations

[zyteka]

Copying data when transforming can be a resource-intensive process. To lay the groundwork for future optimizations, an "inplace" flag should be added to the transformation processes that allows the transformation to happen directly onto the data, without a copy.

[zyteka]

This may not be possible (or at least, its nontrivial) with the way Python handles references. But leaving this here for now for deeper consideration.