Embedded Model Exclude None Not Functioning

# Bug

Using 'exclude_none' in .update function does not work for fields in embedded models

### Current Behavior

Create 'model' with embedded model in field. Use 'exclude_none' in 'model.update(*, exclude_none=True). Field with non-null value becomes null in embedded model.

### Expected behavior

Fields in embedded model should not change from a non-null value to a null if exclude_none is set to True.

### Environment

- ODMantic version: odmantic==0.8.0

Start at the model.update(..., exclude_none=True) path and reproduce the embedded-model case described in the issue. Trace how None values are handled during the update and verify that an existing non-null embedded field remains unchanged when exclude_none is enabled.

Written by the indexing model from the issue text.