Saving progress for datasets

[shahbuland]

Saving progress for datasets, namely IterablePipelines, is currently a bit clunky. The output dataset is agnostic of progress/location in source. With respect to the source iterator being read from, all that is really being saved is an index in the dataset being read from. Currently naively running next on iterator to get back to whatever index was saved. Leaving a note here to revisit this later as it might have unforeseen consequences at scale.

[shahbuland]

#31 Partially addresses, needs more debugging to ensure it is consistent and fault tolerant across all pipelines

[shahbuland]

• Need to add saving for client statistics

[shahbuland]

Solved with #37