perf: use NodeContact instead of Enr for sending talk_req()

[KolbyML]

Description

    pub fn try_from_enr(enr: Enr, ip_mode: IpMode) -> Result<Self, NonContactable> {
        let socket_addr = match ip_mode.get_contactable_addr(&enr) {
            Some(socket_addr) => socket_addr,
            None => return Err(NonContactable { enr }),
        };

        Ok(NodeContact {
            public_key: enr.public_key(),
            socket_addr,
            enr: Some(enr),
        })
    }

Every time we were sending a talk request we were converting the Enr to NodeContact. In doing this operation we call public_key() or in other terms we are recovering the public key every time we send a talk request, in Portal we send all our messages over TalkRequests, currently public_key() is taking over 8.7% of the samples I get from running my benchmark ethereum/trin#1660, by reusing the NodeContact we can avoid repetitively recovering the public key every time

In the benchmark I am sending 6.7GB of block history, so 8.7 percent is fairly significant

Notes & open questions

@jxs @AgeManning @ackintosh ping for review

[AgeManning]

Yep. Typically we know an ENR rather than a NodeContact, which I imagine is why this was the API.

The TalkReq feature as far as I know is mainly used by you guys, so feel free to change the public API.

We will have to make this change with a new version however as it changes the public facing API.