addServer can't parse ipv6 addresses

Problem/Motivation

The addServer() function does not handle IPv6 addresses

https://git.drupalcode.org/project/memcache/-/blob/8.x-2.x/src/Connectio...

Steps to reproduce

Configure settings.php to use ipv6 addresses for memcache servers

Proposed resolution

We should change the parsing to handle IPv6

Remaining tasks

User interface changes

API changes

Data model changes