1) Did you look into the vuln at all?
"...which allows man-in-the-middle attackers to spoof SSL servers via an arbitrary valid certificate."
If you're using ZAP then your MiTM already :)
If you can find some actual impact of this vulnerability to ZAP's users please let us know.
2) The entire networking core is now in an add-on which uses netty and httpcomponents.
The core still contains HttpClient 3.1 for legacy/compatibility reasons.