Halving loop with no plan for odd numbers

shrink_to_one(n) applies the Collatz rule — halve even numbers, and turn odd n into 3n + 1 — counting steps until n reaches 1. shrink_to_one(6) returns 8.

shrink_to_one(8) returns 3, but shrink_to_one(6) hangs. Powers of two work; everything else freezes.