This ensures only Criterion benchmarks get called by `cargo bench`.
Previously, some tests were being loaded too. This is an issue because
if we want to provide command-line arguments to Criterion, it will fail
if we run a non-Criterion benchmark.
We need to specify `harness = false` for each benchmark so that they
don't get wrapped by Cargo, and `bench = false` for everything that
doesn't contain benchmarks but _could_ (i.e. unit and integration
tests). I find Cargo very strange in this regard.
In addition, I fixed the validation benchmark by providing a valid SDL
schema.
V3_GIT_ORIGIN_REV_ID: 338ac5b1411eec7af32923863c5b6f3933c0454b
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## Description
I needed this, so I made it. It's nothing too complex: we just
pretty-print the `schemars` schema for the root `Metadata` type.
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V3_GIT_ORIGIN_REV_ID: a9e75bfa06c35577c17d8cbf0d021b1f56826a28
