feat: Add ShiftLSTM model contribution with tests, docs, and examples

docs/api/models.rst

@@ -30,6 +30,9 @@ routes each feature type automatically.
    * - :doc:`models/pyhealth.models.RNN`
      - Your features are sequences of medical codes (diagnoses, procedures, drugs) across visits
      - One RNN per feature, hidden states concatenated; ``rnn_type`` can be ``"GRU"`` (default) or ``"LSTM"``
+   * - :doc:`models/pyhealth.models.ShiftLSTM`
+     - Your time-series task may exhibit phase-specific or time-varying relationships
+     - Uses segment-specific LSTM parameters; ``num_segments=1`` acts as the shared-parameter baseline
    * - :doc:`models/pyhealth.models.Transformer`
      - You have longer code histories and want attention to capture long-range dependencies
      - Self-attention across the sequence; tends to work well when visit order matters
@@ -174,6 +177,7 @@ API Reference
     models/pyhealth.models.MLP
     models/pyhealth.models.CNN
     models/pyhealth.models.RNN
+    models/pyhealth.models.ShiftLSTM
     models/pyhealth.models.GNN
     models/pyhealth.models.Transformer
     models/pyhealth.models.TransformersModel

docs/api/models/pyhealth.models.ShiftLSTM.rst

@@ -0,0 +1,26 @@
+pyhealth.models.ShiftLSTM
+========================================
+
+
+The segment-wise recurrent layer and the complete ShiftLSTM model.
+
+``ShiftLSTM`` relaxes parameter sharing over time by dividing the sequence
+into ``K`` temporal segments. Each segment uses its own ``LSTMCell`` while the
+hidden and cell states continue flowing through the full sequence. When
+``num_segments=1``, the model reduces to the shared-parameter baseline.
+
+This implementation is inspired by:
+
+  Oh, J., Wang, J., Wiens, J. (2019).
+  "Relaxed Parameter Sharing: Effectively Modeling Time-Varying Relationships
+  in Clinical Time-Series."
+
+.. autoclass:: pyhealth.models.ShiftLSTMLayer
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
+.. autoclass:: pyhealth.models.ShiftLSTM
+    :members:
+    :undoc-members:
+    :show-inheritance: