Suggestions to help debugging slow cell cycles - show last run time

[alefminus]

Description

Currently each cell shows it's run time, so for simple cases where the cell that is slow is obvious you can see by hovering.

But sometimes changing a variable (i.e. a dropdown value) results in a long refresh time that is not just a result of a single cell and it is hard to identify.

Suggested solution

I suggest that hover will show also the last execution time, and/or specifically why it was executed (update to cell X / user request directly).

Alternative

Another option is to use the "explore dependencies" view to also show the last run time. maybe color, or edges, i.e.:
Cell A contains a dependency on a dropdown variable
Dropdown updated -> A recomputed -> B recomputed -> C recomputed
visible by edges from Dropdown cell -> A -> B -> C
always show the last update chain.

Additional context

No response

[mscolnick]

We have improved the dependency viewer to show a dag of the tree - we can add the execution time to this view and hopefully will help debug slow runs/bottlenecks

[mscolnick]

Closing this issue as fixed by #3168