Function compare_implementations 

pub fn compare_implementations<FA, FB, RA, RB>(
    config: &BenchmarkConfig,
    func_a: FA,
    func_b: FB,
) -> CoreResult<ComparisonResult>
where
    FA: FnMut() -> RA,
    FB: FnMut() -> RB,

Compare two implementations using Welch’s t-test on their execution times.

Returns statistics for both plus a significance assessment.