MIMIC4 Readmission Prediction

[EricSchrock]

Overview

This PR updates the readmission_prediction_mimic4_fn for PyHealth 2.0.

In addition to supporting PyHealth 2.0, the new ReadmissionPredictionMIMIC4 task has the following improvements. First, it takes a datetime.timedelta instead of an int for the readmission window, making the input parameter clearer and more flexible. Second, it can optionally exclude patients whose anchor_age is under 18 (a previously unimplemented #todo).

Besides the items listed above, ReadmissionPredictionMIMIC4 should be logically equivalent to readmission_prediction_mimic4_fn.

Testing

I added unit tests for ReadmissionPredictionMIMIC4 and created and ran examples/readmission/readmission_mimic4_rnn.py.

Additional Notes

I also removed the Readmission30DaysMIMIC4 task, since it is pretty much a duplicate of ReadmissionPredictionMIMIC4. The one difference in logic is that Readmission30DaysMIMIC4 excluded visits that lasted 12 hours or less.

I kept this deletion in a separate commit, so if you'd rather keep both, I can easily revert the deletion. If we do keep Readmission30DaysMIMIC4, I'll add some unit tests.

[jhnwu3]

lgtm thanks!