Set node by name

[ollmer]

1. Use names instead of indices in the SetNextNode and everywhere.
2. Remove node counter logic from the tape view. Compute the next intended node in the agent.
3. Track the last used node and the last SetNextNode() step in the view
4. Update all tapes accordingly
5. Rewrite the node intro in the intro.ipynb

[ollmer]

@rizar pls pay special attention to the view.py (I've changed it since our last talk, it uses properties instead of methods again) and intro_clean.ipynb (I've rewritten the nodes intro to reflect addressing by name)

[rizar]

this looks good!

can you please confirm that now control flow steps will remain in the view and should be removed and the time of prompt creation?