Memory leak in optimizeCss

### Link to the code that reproduces this issue https://codesandbox.io/p/devbox/old-currying-xtd57t ### To Reproduce 1. Enable experimental `optimizeCss` 2. Keep the site running for longer time under some traffic 3. Watch the memory grows indefinitely until the app crashes ### Current vs. Expected behavior There's some kind of memory leak when the `optimizeCss` (Critters) is enabled. The memory usage grows linearly to traffic and is not freed, if the pages are SSG. This eventually results in the app crash. ### Verify canary release - [X] I verified that the issue exists in the latest Next.js canary release ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 22.6.0: Wed Jul 5 22:22:05 PDT 2023; root:xnu-8796.141.3~6/RELEASE_ARM64_T6000 Binaries: Node: 16.18.1 npm: 8.19.2 Yarn: N/A pnpm: N/A Relevant Packages: next: 13.5.6 eslint-config-next: N/A react: 18.2.0 react-dom: 18.2.0 typescript: N/A Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Not sure ### Which stage(s) are affected? (Select all that apply) next start (local), Other (Deployed) ### Additional context Memory usage graph of our app: <img width="1255" alt="Zrzut ekranu 2024-01-8 o 15 07 53" src="https://github.com/vercel/next.js/assets/1322846/2dac1a57-8066-4966-bcce-423d4d0b0e6b"> The drops are manual restarts to keep the app running. The moment it finally stabilizes is when we disabled `optimizeCss`.