Summary

This PR simplifies the interface of data processor.

Currently the processor has two interfaces:

nominals, error, history = my_processor.call_with_history(data)
nominals, error = my_processor(data)

to eliminate boilerplate code it internally implements _call_internals method, but its return type will dynamically change depending on input flag.

Details and comments

This PR simplifies the implementation by redefining the history mode as a callback. Namely,

history = DataLogger()

nominals, error = my_processor(data, callback=history)
history.data()

if you don't need history you just

nominals, error = my_processor(data)

so you can use the same interface.