*`DbError::new()` uses generics, which supports old types.

Internal Changes:

* Improve performance of iterator for[`ResultSet<T>`][`ResultSet`] where T is[`Row`]

by sharing an internal fetch array buffer. Before this change, one row in the buffer

is copied to`Row` for each iteration. After this, new fetch array buffer is allocated

when more rows must be fetched into a buffer but the buffer is referenced by`Row`s.

Breaking changes:

fnfetch_rows_to_vec() ->Result<()>{

let conn = test_util::connect()?;

letmut stmt = conn

.build()?;

letmut rows =Vec::new();

for row_resultin stmt.query(&[])?{

rows.push(row_result?);

for(index, row)in rows.iter().enumerate(){

let int_col:usize = row.get(0)?;

assert_eq!(int_col, index +1);