test(vitest-plugin): add with-vitest-v4 example

Now that the plugin's own dev dependency tracks Vitest 5, add a dedicated
Vitest 4 example so the legacy (v3/4) benchmark seam keeps explicit coverage
alongside the existing with-vitest-v3 example. Mirrors that example, pinning
vitest ^4.1.9.

Refs COD-2931
Co-Authored-By: Claude <noreply@anthropic.com>

Author: GuillaumeLagrange

examples/with-vitest-v4/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "with-vitest-v4",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "bench-vitest": "vitest bench --run"
+  },
+  "devDependencies": {
+    "@codspeed/vitest-plugin": "workspace:*",
+    "typescript": "^5.1.3",
+    "vitest": "^4.1.9"
+  }
+}

examples/with-vitest-v4/src/fibonacci.bench.ts

@@ -0,0 +1,20 @@
+import { bench, describe } from "vitest";
+import { iterativeFibonacci, recursiveFibonacci } from "./fibonacci";
+
+describe("fibonacci", () => {
+  bench("recursive fibo 15", () => {
+    recursiveFibonacci(15);
+  });
+
+  bench("recursive fibo 20", () => {
+    recursiveFibonacci(20);
+  });
+
+  bench("iterative fibo 15", () => {
+    iterativeFibonacci(15);
+  });
+
+  bench("iterative fibo 20", () => {
+    iterativeFibonacci(20);
+  });
+});

examples/with-vitest-v4/src/fibonacci.ts

@@ -0,0 +1,17 @@
+export function recursiveFibonacci(n: number): number {
+  if (n < 2) {
+    return n;
+  }
+  return recursiveFibonacci(n - 1) + recursiveFibonacci(n - 2);
+}
+
+export function iterativeFibonacci(n: number): number {
+  let a = 0;
+  let b = 1;
+  for (let i = 0; i < n; i++) {
+    const temp = a + b;
+    a = b;
+    b = temp;
+  }
+  return a;
+}

examples/with-vitest-v4/tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "compilerOptions": {
+    "lib": ["es2023"],
+    "module": "ESNext",
+    "verbatimModuleSyntax": true,
+    "target": "es2022",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "moduleResolution": "Node"
+  }
+}

examples/with-vitest-v4/vitest.config.ts

@@ -0,0 +1,6 @@
+import codspeedPlugin from "@codspeed/vitest-plugin";
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  plugins: [codspeedPlugin()],
+});