Fhir-core

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- Nothing changed yet.

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Fixes

- External issue https://github.com/nazrulworld/fhir.resources/issues/175

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- **XML serialization/deserialization support has been added**.

- Remove dependency on `typed-ast` as it is not needed and won't work in later Python versions.

- Fix typo in test case.

- Raising 'ValueError' has been suspended inside Fhir Model Validation 'fhir_model_validator()', if None value is provided.

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- Improves missing value validation message, as error type is now ``model_field_validation.missing``.

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- Improve validation error message.

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- Version policy updated, now `.bx` suffix has been removed.

Fixes

- Business logic for None type validation against FHIR Model validator as None value is acceptable! Instead, you should make Pydantic field optional.