Save perf_q to database

[abrichr]

This task involves creating a model and saving events from perf_q in record.py:

https://github.com/MLDSAI/puterbot/blob/main/puterbot/record.py#LL591C10-L591C10

[abrichr]

@apgorton thank you for finding the source of #93 ! I believe this is the solution. Let's treat performance events just like Screenshots/InputEvents/WindowEvents and save them to a new table. That way there won't be any special queue left over when everything is shutting down and that problem goes away.

What do you think?

This involves:

1. Create a PerformanceEvent model in models.py
2. Implement a perf_queue_writer analogous to the other writers in record.py
3. Modify plot_performance to retrieve the saved performance values

This will also set us up nicely for #73

[apgorton]

I think this approach would address #93 and is a good way to do that while implementing this one. I'll make the changes.