Function non_nullable_position_checks 

fn non_nullable_position_checks(param_types: &[Type]) -> Vec<TokenStream>

Generates per-position nullability checks for non-nullable parameters.

For each parameter that rejects NULL (not Option, not OptionalArg<Option<..>>), generates a check that the corresponding input position is nullable. For Variadic<T> with non-nullable T, generates a check over all remaining input positions.