Core: Refactor ZMQ usage into ZMQService

[zach2good]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

This does a few things:

• Refactor ZMQ lifecycle to be a part of the application-owned ZMQService, which has one dedicated ZMQ I/O thread
• Rather than polling and sleeping manually, we use zmq_poll
• We pass around "Channels": non owning references to the in/out queues to our sockets, etc.
• I work a little bit on un-staticing some of our ZMQ stuff, but that's a job for another day
• For xi_test: We were making and using tcp sockets and there was some world/map/test conflict. In the test setup we now use inproc transport, so there's no chance of collisions and the lifetimes are much more resiliant
• EDIT: This also means that the minimum 2* 200ms round trip latency for IPC is reduced to an average <100ms total, or whatever ZMQ promises and what our tick handling will allow. Faster chat, faster IPC, etc.

[zach2good]

Nothing spinning:

[zach2good]

Testing:

• Login and zoning requires round-trip IPC, etc. logging in and zoning around still works, as does yelling

EDIT: And is faster!