macro for bench cases

Hi there,

I really like this plugin. Not sure if this already exists, anyways I did not find it: Did you ever consider to extend or clone this crate to create cases for benchmarks as well? It would be really helpful to bechmark different implementations of an algorithm or the effect of different inputs to a function (for example length of a String that shall be manipulated).

The issue proposes extending or cloning this Rust crate to create benchmark cases, but names no files, tests, or entry points. First clarify whether benchmark support belongs in this crate and define the expected support for comparing implementations and varying inputs before identifying an implementation path and acceptance tests.

Written by the indexing model from the issue text.