Change header size limits
When I received the response with HttpClientRequestRef, I received a Buffer limit reached error.
I think the cause is that the header size is too large, but is it possible to change the limit?

```nim
let session = HttpSessionRef.new()

# It's actually a different URL.
let address = session.getAddress("https://example.com").get

let client = HttpClientRequestRef.new(session, address, MethodHead)

let response = await client.send
```

```
Error: unhandled exception: Could not read response headers, reason: Buffer limit reached [HttpReadError]
```

I confirmed that Python [requests](https://pypi.org/project/requests/) can be received normally.