Wsgo

Add workaround for for segfaults caused by faulthandler generating stack traces without holding the GIL, so sometimes the thread state or stack frame data would be freed whilst it was being traversed. Now uses `faulthandler.dump_traceback` directly with the GIL held.

(see https://github.com/python/cpython/issues/116008)

- Tune rate limiting, consider each IPv6 /64 as a single user
- Finalize on shutdown so that atexits are called

- Fix gateway timeout handling and responses

- Disabled caching-by-default, responses require a max-age to be cached
- Added support for Python 3.12
- Report request/error/timeout/drop counts via SIGUSR2
- Minor optimisations

- Add readline to wsgi.input for Django >4.2 compatibility
- Add request parking mechanism for long-polling
- Safer X-Forwarded-For header handling
- Reader/writer buffering changes

- Rewrite prioritising scheduler to be simpler and more predictable
- Wait for running background tasks to finish (within timeout) before exiting
- Cleanup