ci: add test-unit + bench (smoke) jobs

- test-unit: runs 'zig build test-unit' so host-side Zig unit tests
  are exercised in CI (matches feat/string-builtins and
  feat/composite-ref-iteration).
- bench: runs 'zig build bench' (Node-driven, ~22000 evaluations
  total over 2 fixtures) and prints the latency table to the run
  log. Not gated; the goal is visibility, not perf-regression
  enforcement (CI runners have variable noise floors).

Author: kanywst

.github/workflows/ci.yml

@@ -54,6 +54,24 @@ jobs:
       - name: zig build test-unit
         run: zig build test-unit
 
+  bench:
+    name: bench (smoke)
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - uses: mlugg/setup-zig@d1434d08867e3ee9daa34448df10607b98908d29 # v2.2.1
+        with:
+          version: 0.16.0
+
+      - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
+        with:
+          node-version: 22
+
+      - name: zig build bench
+        run: zig build bench
+
   test-node:
     name: test (node)
     runs-on: ubuntu-latest