cell execution time information -- make compatible with upstream

[williamstein]

Just saw this:

jupyter/nbformat#144

We could change our code, which also stores timing, to be compatible.

[williamstein]

Yes, we should definitely try to do this!

[williamstein]

I just looked and our cell timing implementation right now SUCKS! I don't know what happened, but it's really bad because the information about when a cell was executed and how long it took to compute is actually stored nowhere! If you refresh your browser it is just gone. That's terrible.

So adding the info in the same way as in jupyterlab and also just storing it at all is something we definitely need to do soon.

[williamstein]

I was fortunately just completely wrong in my comment #3983 (comment) since the start and end time are stored in our core notebook data structure:

We know when the cell was run, when it stopped running, and it is all persisted. It's in the start/end fields.

Also, the upstream execution time is defined here https://github.com/jupyter/nbformat/blob/main/nbformat/v4/nbformat.v4.5.schema.json#L223
but it seems to be really low level and far too detailed. There can be hundreds of messages for a given cell output, and storing all that is something nobody needs, at least not by default. So we're storing something much, much simpler in cocalc, hence there's no compatibility to be gained here. Closing.