Add next-visit diagnosis prediction task

[Joshua-Van-Rossum]

new task function for next-visit diagnosis prediction, which uses a patient's complete visit history to predict diagnoses that will occur in their next hospital admission.

-Datasets Supported: MIMIC-IV, MIMIC-III, eICU

• Features:
  • Historical diagnosis codes from all previous visits
  • Historical procedure codes (optional)
  • Time gaps between visits (optional)
• Label: Diagnosis codes from the next visit

Testing uses artificial Patient object