reuse devcontainer image in github actions

This is needed to run benchmarking tests in CI using the same `valgrind` binaries we install in the devcontainer.
Also moved the cache steps to a common action to avoid duplication.

TODO: stash the changesets

.github/actions/cache/restore/action.yml

@@ -0,0 +1,18 @@
+name: "cache/restore"
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Restore Cache"
+      uses: "actions/cache/restore@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9"
+      with:
+        # __SLANG_CI_CACHE_PATHS__ (keep in sync)
+        key: "cache-${{ github.ref_name }}-${{ hashFiles('Cargo.lock') }}-${{ hashFiles('package-lock.json') }}"
+        path: |
+          ~/.cache/hermit/
+          ~/.local/share/virtualenvs/
+          .hermit/
+        restore-keys: |
+          cache-${{ github.ref_name }}-
+          cache-main-
+          cache-

.github/actions/cache/save/action.yml

@@ -0,0 +1,18 @@
+name: "cache/save"
+
+runs:
+  using: "composite"
+  steps:
+    - name: "Repossess files from devcontainer user"
+      shell: "bash"
+      run: "sudo chown -R $USER:$USER $GITHUB_WORKSPACE"
+
+    - name: "Save Cache"
+      uses: "actions/cache/save@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9"
+      with:
+        # __SLANG_CI_CACHE_PATHS__ (keep in sync)
+        key: "cache-${{ github.ref_name }}-${{ hashFiles('Cargo.lock') }}-${{ hashFiles('package-lock.json') }}"
+        path: |
+          ~/.cache/hermit/
+          ~/.local/share/virtualenvs/
+          .hermit/

.github/workflows/benchmark.yml

@@ -0,0 +1,42 @@
+name: "benchmark"
+
+on:
+  # Run using manual triggers from GitHub UI:
+  # https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
+  workflow_dispatch: {}
+
+  # Run on pushes to any branch:
+  push: {}
+
+# Queue up benchmark workflows for the same branch, so that results are reported in order:
+concurrency:
+  group: "${{ github.workflow }}-${{ github.ref_name }}"
+  cancel-in-progress: false
+
+jobs:
+  run:
+    runs-on: "ubuntu-22.04" # _SLANG_DEV_CONTAINER_BASE_IMAGE_ (keep in sync)
+
+    # Only run on the main repo (not forks):
+    if: "${{ github.repository == 'NomicFoundation/slang' }}"
+
+    steps:
+      - name: "Checkout Repository"
+        uses: "actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332"
+
+      - name: "Restore Cache"
+        uses: "./.github/actions/cache/restore"
+
+      - name: "infra setup cargo"
+        uses: "./.devcontainer"
+        with:
+          entrypoint: "./scripts/bin/infra"
+          args: "setup cargo"
+
+      - name: "infra perf benchmark"
+        uses: "./.devcontainer"
+        with:
+          entrypoint: "./scripts/bin/infra"
+          args: "perf benchmark"
+        env:
+          BENCHER_API_TOKEN: "${{ secrets.BENCHER_API_TOKEN }}"