>Fixes bugs/regressions quickly (time spent)
Do the least possible to make it work again, don't investigate or fix the underlying confusion or low-quality subsystem that made it break. Volunteer for bug fix tasks that look easy, stay away from the ones that look hard.
>Creates test plans (number of plans created)
Write low-effort test plans.
>Helps with recruiting (number of candidates interviewed)
Give lots of interviews without really paying attention.
>Helps guide other merge requests to completion (number of merges)
Get your friends to split all their changes into the smallest possible merge requests so you can accept as many as possible.
>Provides thorough and timely code feedback for peers (time between commit and feedback)
Provide rapid but low-effort feedback.
Metrics-driven management is cancer and you should run, not walk, from any organization that expresses any inkling of interest in it.
You (in general, not parent specifically) are almost certainly not smart enough to create an quantitative incentive system that actually produces the behavior you want, rather than the appearance of it. Respect the difficulty of the task, and don't.