feat: more from impls for ServerName and IpAddr

[nanoqsh]

Let's add more convenient From impls.

Now instead of:

let name = ServerName::IpAddress(IpAddr::V4(Ipv4Addr::LOCALHOST).into());

You can write:

let name = ServerName::from(Ipv4Addr::LOCALHOST);

[djc]

Makes sense to me, thanks!

[djc]

Reminder that while core::net now contains IpAddr et al, that's a relatively recent development as of 1.77.0, which is why, given our MSRV, we still need to duplicate a bunch of stuff here and guard trait impls with std here.

[cpu]

Thank you, this is a nice quality of life boost.