Update http.zig max_simultaneous_requests from 256 to 65535 for default NodeJS like request behavior.

[metaspartan]

Update http.zig max_simultaneous_requests from 256 to 65535 for default NodeJS like request behavior.

What does this PR do?

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

[Jarred-Sumner]

I'm not sure this is the right default for fetch. Your operating system has an upper limit of something like 16,000 - 64,000 maximum open sockets unless you manually configure linux to behave otherwise.

If any of the requests are short-lived, it also prevents HTTP Keep Alive from kicking in

https://example.com:

Elapsed	Limit
5.27s	9999
2.26s	256 (default)

http://example.com:

Elapsed	Limit
5.20s	9999
2.26s	256 (default)

const p = []
for (let i = 0; i < 1000; i++) {
  p.push(fetch('https://example.com/').then(re => console.count("Completed")));
 }
 await Promise.all(p);

It feels like we could address this more effectively with smarter scheduling.

That being said, if it's a loopback address maybe we shouldn't rate limit at all