Add interface to load experiments lazily from a query

[vnmabus]

A common pattern when loading experiments is to pick some data for each experiment (such as the accuracy) and process it for each experiment (for example, storing it into a dataframe).

With the current code, in order to do that we have to first load all experiments into memory and then iterate over them. This is memory-expensive, and I had not enough memory in my machine for doing that for a (rather large) collection of experiments.

However, a lazy way to iterate over the experiments in the query can be provided, so that only one experiment needs to be created at a time.