[Feature] New data backend for QD Merlin Medipix

• For better performance and stability, the new QD Merlin Medipix backend is re-written in rust, see https://github.com/LiberTEM/LiberTEM-rs/pull/65 for the rust side. Both the Python and rust sides have been refactored to be more generic, such that adding support for new (frame-based) detectors is easier (#161, #160).