Move benchmarks to a new ring-bench crate.

Move the Criterion.rs dependency out of *ring* into a new `ring-benches`
crate. This speeds up many build scenerios by eliminating a bunch of
dependencies from *ring*'s dependency tree for `cargo test`.

.github/workflows/ci.yml

@@ -155,6 +155,7 @@ jobs:
       - run: sh mk/package.sh
         shell: bash
 
+  # Intentionally excludes benchmarks for build performance reasons.
   test:
     # Don't run duplicate `push` jobs for the repo owner's PRs.
     if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
@@ -322,6 +323,28 @@ jobs:
                 (!contains(matrix.host_os, 'macos') || matrix.mode != '--release') }}
         run: mk/check-symbol-prefixes.sh --target=${{ matrix.target }}
 
+  test-bench:
+    # Don't run duplicate `push` jobs for the repo owner's PRs.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
+
+    runs-on: ubuntu-22.04
+
+    steps:
+      - run: sudo apt-get update -y
+
+      - uses: briansmith/actions-checkout@v2
+        with:
+          persist-credentials: false
+
+      - run: mk/install-build-tools.sh --target=x86_64-unknown-linux-gnu
+
+      - uses: briansmith/actions-rs-toolchain@v1
+        with:
+          override: true
+          toolchain: stable
+
+      - run: cargo test -p ring-bench --all-features --all-targets
+
   # XXX: GitHub Actions won't let us test all the combinations of features in
   # the "test" matrix because the resultant matrix would be larger than the
   # maximum they allow.

Cargo.toml

@@ -192,9 +192,6 @@ libc = { version = "0.2.100", default-features = false }
 [build-dependencies]
 cc = { version = "1.0.69", default-features = false }
 
-[dev-dependencies]
-criterion = { version = "0.4", default-features = false }
-
 [features]
 # These features are documented in the top-level module's documentation.
 default = ["alloc", "dev_urandom_fallback"]
@@ -225,10 +222,9 @@ lto = true
 debug-assertions = false
 codegen-units = 1
 
-[[bench]]
-name = "aead"
-harness = false
-
-[[bench]]
-name = "x25519"
-harness = false
+[workspace]
+members = [
+    # intentionally not a default member so that `cargo test` doesn't cause criterion.rs and all its
+    # dependencies to get built.
+    "bench",
+]

bench/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+edition = "2021"
+name = "ring-bench"
+publish = false
+version = "0.1.0"
+
+[dependencies]
+ring = { path = "../" }
+
+[dev-dependencies]
+criterion = { version = "0.4", default-features = false }
+
+[[bench]]
+name = "aead"
+harness = false
+path = "aead.rs"
+
+[[bench]]
+name = "x25519"
+harness = false
+path = "x25519.rs"