Update benchmarks to Benchmarking V2

[HCastano]

Looks like there's a new version of the benchmark macros which uses procedural macros instead
of declarative macros. Not exactly sure when this was introduced, but it looks like it
happened some time last year.

There's no rush to upgrade, but it would be nice to switch since we'd get some nice QoL
features like better IDE support and code formatting.