example: use the experimental cbv_decide tactic to check if a number is a prime power

[wkrozowski]

This PR provides an example use of the experimental cbv_decide tactic on nightly-2026-02-16 on the following example:

import Mathlib.Algebra.IsPrimePow

example : IsPrimePow 10093 := by decide_cbv

example : IsPrimePow 100999 := by decide_cbv

example : ¬ IsPrimePow 15 := by decide_cbv

example : ¬ IsPrimePow 111111111111111155 := by decide_cbv