refactor(odbc): store nullability separately

This commit refactors the OdbcValueVec enum by removing nullable variants and consolidating the handling of null values into a separate nulls vector. The conversion function for AnySlice is updated to return both the value vector and the nulls vector, improving the overall structure and clarity of the code. Additionally, the value retrieval methods are simplified to utilize the new nulls handling approach.

Author: lovasoa

sqlx-core/src/odbc/connection/odbc_bridge.rs

@@ -286,8 +286,10 @@ where
 fn create_column_data(slice: AnySlice<'_>, type_info: &OdbcTypeInfo) -> Arc<ColumnData> {
     use crate::odbc::value::convert_any_slice_to_value_vec;
 
+    let (values, nulls) = convert_any_slice_to_value_vec(slice);
     Arc::new(ColumnData {
-        values: convert_any_slice_to_value_vec(slice),
+        values,
         type_info: type_info.clone(),
+        nulls,
     })
 }