Support reading variables from multiple runs in parallel #468
Description
I've recently had to combine pulse-resolved variables from multiple runs for a few proposals, and noticed that the time it takes to read them really adds up fast. It would be nice if we could support reading variables from multiple runs and parallelize it automatically for the users. I did play around with reading in parallel with a threadpool but that didn't seem to help, not sure why since I thought that the HDF5 lock is per-file.