Function validate_and_normalize_annotation 

pub(crate) fn validate_and_normalize_annotation(
    family: AnnotationFamily,
    cx: &AnnotationContext<'_>,
    key: &str,
    value: &str,
) -> Result<String, AnnotationValidationError>

Validates one annotation option and returns the value to store — the repartition hint is trimmed to the bare column name, semantic values pass through unchanged.