feat(benchmark infra) Add beforeEachBatchAsync callback

[markfields]

Description

Fixes AB#19814

This adds an async version of beforeEachBatch, to allow awaiting async code before running a batch of benchmark cycles.

[alexvy86]

IIRC there's a pattern somewhere in the benchmark package on how to use the sync VS async functions. I'm not sure I agree with just replacing beforeEachBatch with beforeEachBatchAsync withing runBenchmarkAsync is the right way to go. If the beforeEachBatch function is not async but the benchmarkFn is, I think it's still valid to use sync beforeEachBatch inside runBenchmarkAsync, unless we rewrite the contracts and the docs a bit, so BenchmarkRunningOptionsAsync can only take the async version of everything.

Depending on the final way we go, we might need to document this as a breaking change for the package (bump version to 0.52 and add an entry to CHANGELOG.md). Related: I think somewhere I might have a branch with the updated CHANGELOG that includes the changes in 0.51, I'll see if I can find it.

[markfields]

If the beforeEachBatch function is not async but the benchmarkFn is, I think it's still valid to use sync beforeEachBatch inside runBenchmarkAsync,

You're so right! I thought about this briefly then promptly forgot. Should I run both beforeEachBatch's in the async case...?