Step-in feature into pattern execution

[shinich1]

Is your feature request related to a problem? Please describe.
no

Describe the solution you'd like
It might be beneficial if pattern execution can be done by hand, i.e. if you can execute only up to certain command, check the state, and step forward the command execution, etc.
This is particularly important if error corrections will be implemented (with density matrix backend).

Describe alternatives you've considered
na

Additional context
na

[shinich1]

we can have an internal variable to keep track of the execution progress, and have methods run_command() and run_commands(N), print_state(), print_measurement_results(), etc.

[shinich1]

also add verbosity option to pattern execution

[thierry-martinez]

Would be part of #388.

[thierry-martinez]

#388 allows step-in execution but only graphically and not necessarily interactively (the simulation is performed before the visualization). We still would like non-graphic interactive execution.

[emlynsg]

Idea is another class in simulator module, idea is to use to debug things:

• Choice of backend for "state" and node numbers at each step
• Ability to step back and forth (inversion of control)
• Want to choose branches

Consider building the visualisation on top of this.