Add introspection to processing data accessor
Split the pipeline concept into:
- Computation, with resources that are local to the processing such as GPU memory are bound to the computation lifetime
- Data accessor/publisher, with circuclar buffer and progress counter that are available until the pipeline get erased.
Data accessors should be introspectable and give information about the data available (shape, dtype...).They are basically the sender part of the channel where the receiver is in the reading loop of Bliss.