Native fetch leaks memory on Node v19+

1. Install Docker
2. Install Node v20+ and run npm install
3. Install K6 (or use any other load testing tool)
4. Spin up httpbin: docker run --rm -p "58080:8080" mccutchen/go-httpbin
5. Run a simple http server in debug mode: npm run debug:native (or npm run debug:undici)
6. Warm up the server: k6 run k6.js --vus 5 --duration 10s
7. Run first set of requests: k6 run k6.js --vus 5 --duration 360s and make the heap snapshot
8. Run second set of requests: k6 run k6.js --vus 5 --duration 360s and make the heap snapshot

Summary

Requests made	v20.2 + fetch	v20.2 + undici v5.22.1	v18.16 + fetch	v18.16 + undici v5.22.1
~300k	16MB	19MB	9MB	11MB
~600k	23MB	26MB	9MB	11MB

Node v20.2

native fetch

Requests made	Memory	Step number	Heap snapshot
295k	16MB	7	node-20.2-5vus360s (1).heapsnapshot
575k	23MB	8	node-20.2-5vus360s (2).heapsnapshot

undici

Requests made	Memory	Step number	Heap snapshot
356k	19MB	7	node-20.2-5vus360s_undici (1).heapsnapshot
650k	26MB	8	node-20.2-5vus360s_undici (2).heapsnapshot

Node v18.16

native fetch

Requests made	Memory	Step number	Heap snapshot
360k	9MB	7	node-18.16-5vus360s (1).heapsnapshot
680k	9MB	8	node-18.16-5vus360s (2).heapsnapshot

undici

Requests made	Memory	Step number	Heap snapshot
366k	11MB	7	node-18.16-5vus360s_undici (1).heapsnapshot
678k	11MB	8	node-18.16-5vus360s_undici (2).heapsnapshot