chore: replace import from chai with import from vitest

tests/utils/mock.ts

@@ -3,7 +3,7 @@ import type { Request, Response } from "@tinyhttp/app"
 import { parse } from "@tinyhttp/cookie"
 import { cookieParser, signedCookie } from "@tinyhttp/cookie-parser"
 /* eslint-disable @typescript-eslint/no-unsafe-assignment */
-import { assert } from "chai"
+import { assert } from "vitest"
 import { COOKIE_SECRET, HEADER_KEY } from "./constants.js"
 import { getCookieFromRequest, getCookieValueFromResponse } from "./helpers.js"