Clean up reader-mapper-parser infrastructure, use multiformat reader

[lukaspie]

Currently, the reader implements a three-layer structure:

• there is the XpsReader(BaseReader)
• then there's a layer called "mappers" (see here for an example)
• these mappers themselves actually call "parsers" (example).

The mappers are used for one file format (like the sle format from SPECS) and then I have a logic that calls a parser for a specific subsets of such files, e.g. depending on the software version that was used for this file. That allows me to keep functionality across different, yet very similar versions of a format by inheritance and abstract base classes.

All of those sub-classes could be readers themselvers, inheriting from our BaseReader class (or the MultiFormatReader developed in FAIRmat-NFDI/pynxtools#250).

The file extension is often not unique, i.e., many vendors have a .txt export, but all the files are actually different. But this logic could probably be handled by passing a function in the extensions dict of the MultiFormatReader that does this. This is already being handled similary. And finally, there should be be a check that the file comes from the list of supported vendors.