Function parse_dataframe_attrs 

fn parse_dataframe_attrs(input: &DeriveInput) -> Result<DataFrameAttrs>

Parse container-level #[dataframe(...)] attributes from the derive input.

Supported keys:

• name = "CustomName" – custom companion type name (default: {TypeName}DataFrame)
• align – enum alignment mode (field-name union across variants)
• tag = "col_name" – add a variant discriminator column (works on both structs and enums)
• conflicts = "string" – coerce type-conflicting columns to String via ToString

Returns Err for unknown keys or non-string-literal values.