Make a decision whether we should enable `TCP_NODELAY` by default or not

> The problem here should be related to Nagle’s algorithm, i.e. the `TCP_NODELAY` option.
> On Node.js, it's enabled by default: https://nodejs.org/api/http.html#httpcreateserveroptions-requestlistener
> On actix-web (actix-http), it's disabled by default (no config).
> I've tested on your benchmark and confirmed enabling it via `actix_tls` resolved the latency difference.
> Maybe we should make it enable by default, but it's a behavior change and should happen on major release.
> For now, I'm going to add a helper method to enable it easily.

_Originally posted by @JohnTitor in [#3841](https://github.com/actix/actix-web/issues/3841#issuecomment-3883169095)_