Implement first() for easy retrieval of single-row results

[evyatark2]

No description provided.

[speed2exe]

@evyatark2 We should move this logic to line 147 instead, so that there won't be a need for if statement, something like:

            switch (row_res) {
                .ok => return null,
                .err => |err| return err.asError(),
                .row => |row| {
                    const i = r.iter();
                    while (try i.next()) |_| {}
                    return row
                },
            };

[speed2exe]

@evyatark2 We should also add a simple test case that returns 2 rows e.g. SELECT 1 UNION ALL SELECT 2, then call this method, ping the connection after (make sure that the connection is working normally after query).

[speed2exe]

LGTM