Add eval socket compatibility shim for haxe 4.2+

[dimensionscape]

Adds an eval socket shim using eval.luv, while keeping the existing sys.net.Socket path for other targets and older Haxe versions.

Also adds a small socket compatibility test and a test for for the issue highlighted in HaxeFoundation/haxe#12958

You may want to shadow sys.net.Socket entirely but I thought this was perhaps a little bit cleaner. EIther way, it's a public API decision.

[joshtynjala]

Thanks!

Ideally, I'd like to do something like this:

#if (eval && (haxe_ver >= 4.2))
import snake._internal.net.Socket;
#else
import sys.net.Socket;
#end

If both classes have the same public API, nothing else in the existing code should need to change except which class gets imported.

It should be fairly easy for me to modify the code from your PR to do that. I might not have a chance to dig into it right away, though, so feel free, if you feel like scratching that itch. I'll probably find a moment later this month, though.