Add image re-encoding benchmarks.

This is one of the more compute-heavy workflows that the
app server performs, we should be able measure how fast it is
against past revisions.

Add a step to the general CI job which will run each benchmark
as a test without trying to actually measure many iterations.

.github/workflows/rust-ci-full.yml

@@ -30,6 +30,8 @@ jobs:
           components: rustfmt
       - name: cargo fmt
         run: cargo fmt -- --config imports_granularity=Item --check
+      - name: Rust benchmark smoke test
+        run: ../scripts/smoke-test-rust-benches.sh
 
   cargo_shear:
     name: cargo shear

.github/workflows/rust-ci.yml

@@ -72,6 +72,8 @@ jobs:
           components: rustfmt
       - name: cargo fmt
         run: cargo fmt -- --config imports_granularity=Item --check
+      - name: Rust benchmark smoke test
+        run: ../scripts/smoke-test-rust-benches.sh
 
   cargo_shear:
     name: cargo shear