@bwalsh re-writing GDC. hold on to the review.

noted this new criterion

1 validation error for DocumentReference
content.0.attachment.size
Input should be less than or equal to 2147483647 [type=less_than_equal, input_value=107991595707, input_type=int]
For further information visit https://errors.pydantic.dev/2.10/v/less_than_equal

for bioinformatics files like this bems file the size is ~107GB where the new content.0.attachment.size limit is now 2GB

converting size from bytes to MB to surpass 2GB min file-size in (Pydantic 2.10 - FHIR 8.0.0 requirement)
alternatively it could be placed the file size in Observation focus -> DocumentReference

@bwalsh it's ready for another review. what worries me about this new version:

1. serialization issues. Noted the types are converted to str. tried to cast to int for example, but the model_dum() function seems to have some new serialization features.

fhirizer/venv/lib/python3.13/site-packages/fhir_core/fhirabstractmodel.py:427: UserWarning: Pydantic serializer warnings:
    Expected `Observation` but got `dict` with value `{'reference': 'Observatio...5b1d-a199-a07cc2adaa7c'}` - serialized value may not be as expected
    return serialize(value)

Passes g3t validation.

3. The DocumentReference.content.[0].attachment.size now has a 2GB limit. I converted all the file sizes to MB for now.