The PR fixes#40066.
Next.js' `serveStatic` method is powered by the [send](https://github.com/pillarjs/send) module, which could throw errors under specific circumstances.
Currently, Next.js only preserves the 412 Error from send, hence issue #40066 (where 416 Error is not preserved).
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
The PR fixes#39706 by adding `avif` mime type directly to `send`. The PR also removes the previous avif workaround for image optimizer.
Note: The PR is still a workaround for now. I will submit a PR to `pillarjs/send` to help them update `mime` to fix the issue once and for all. But now `send.mime.define` just works.
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
