Type discrepancy between QueryRowsResult::column_specs and PreparedStatement::get_result_set_col_specs

[muzarski]

The former returns ColumnSpecs<'_>, while the latter returns &[ColumnSpec<'_>].

In a sense, returned values represent the same thing - thus, the returned types should be the same or easily convertible into one another (currently ColumnSpecs constructor is pub(crate)).

[Lorak-mmk]

One tiny problem with this. ColumnSpecs wrapper assumes that the lifetime of inner ColumnSpec is the same as the lifetime of the slice itself:

#[derive(Debug, Clone, Copy)]
pub struct ColumnSpecs<'res> {
    specs: &'res [ColumnSpec<'res>],
}

If we change the return type of PreparedStatement::get_result_set_col_specs to ColumnSpecs, then it sadly no longer returns ColumnSpec<'static> - it is limited to the lifetime of self.
How should we address this? And is the wrapper even necessary given that we gave up the idea of eliminating TableSpec from binding markers in prepared statement? @wprzytula