Node v16 vs v20/v21 regression on http perf

This server:

'use strict'

const server = require('http').createServer(function (req, res) {
  res.setHeader('content-type', 'application/json; charset=utf-8')
  res.end(JSON.stringify({ hello: 'world' }))
})

server.listen(3000)

gives me around 55k req/s on v21, v20, v18, while it gives me 65k req/s in v16 and v14.

I use the following to test but you should be able to get similar results with wrk too:

autocannon -c 100 -d 5 -p 10 -W [ -c 10 -d 2 -p 2 ] localhost:3000

This might be due to #79.

Start by running the provided HTTP server benchmark with Node v16, v18, v20, and v21 using the listed autocannon command, then compare the results with wrk if needed. Read issue #79 for related context and identify the cause of the throughput regression; done means the regression is explained and an appropriate fix or follow-up is established.