Understanding the structure of TRD2D.

This MR contains a slightly restructured version of CbmTrdUnpackFaspAlgo which was created as part of my ongoing efforts to understand TRD2D unpacking, as a precursor to the implementation of an online-capable unpacker for TRD2D in cbm::algo.

The code here is not meant to actually be merged into the master branch. The main purpose of this MR is to provide a platform to discuss details of the unpacker code with @a.bercuci with specific code examples.