Add Bencher to track benchmarks in CI

@epage thank you for [the mention](https://news.ycombinator.com/item?id=42079137) earlier this week. I wanted to follow up as a lot of progress has been made since we last spoke. Bencher can now create all dimensions on-the-fly, so there is no more need to make them in advance. Further, you can now configure everything, including [setting thresholds](https://bencher.dev/docs/explanation/thresholds/) using the CLI. This should make it possible to use the same template across repos. The only thing to parameterize is the project slug. Are you still using Divan as your benchmarking harness? @nvzqz [mentioned back in June](https://github.com/bencherdev/bencher/issues/321#issuecomment-2198512736) that the JSON output should be coming "soon". Bencher now also supports [tracking compile times](https://bencher.dev/docs/how-to/track-build-time/) and [tracking binary size](https://bencher.dev/docs/how-to/track-file-size/), if either of those are also of interest.