[CS 598] Add LSTM Model

[bmalis2]

Type: Model Contribution Net IDs: bmalis2, divyesh3 Paper: Addressing Wearable Sleep Tracking Inequity: A New Dataset and Novel Methods for a Population with Sleep Disorders Paper Link: https://proceedings.mlr.press/v248/wang24a.html

Description: Implements a LSTM model class and a helper function test_lstm to test the class.

Model: pyhealth/models/lstm.py Test: function test_lstm

Model can be tested with python pyhealth/models/lstm.py