Absolute difference and relative lift

Maybank tested a redesigned loan application form. "It went up 1.2 points" and "it went up 18%" are different claims about the same result, and stakeholders confuse them constantly.

From ab_results, return a single row with:

- abs_diff — treatment rate minus control rate, rounded to 4 decimal places - relative_lift — that difference as a fraction of the control rate, rounded to 4 decimal places