This enum allows the user to control how Criterion.rs chooses the iteration count when sampling.
The default is Auto, which will choose a method automatically based on the iteration time during
the warm-up phase.
Scale the iteration count in each sample linearly. This is suitable for most benchmarks,
but it tends to require many iterations which can make it very slow for very long benchmarks.
Keep the iteration count the same for all samples. This is not recommended, as it affects
the statistics that Criterion.rs can compute. However, it requires fewer iterations than
the Linear method and therefore is more suitable for very long-running benchmarks where
benchmark execution time is more of a problem and statistical precision is less important.