Fixed crash on new Chromium context

[diefbell-grabcad]

Attempts to address: #663

It persists the default ZMQ Context across Chromium contexts.

I barely understand this stuff, so this may be completely wrong. Also some of the tests fail for worker pools. Not sure if that's my dev environment or an actual issue I've caused 🤷

Draft PR because, like I said, no idea if this is "correct" and should actually be merged yet..

[diefbell-grabcad]

According to the Node documentation for context-aware addons:

Since the addon may be loaded multiple times, potentially even from different threads, any global static data stored in the addon must be properly protected, and must not contain any persistent references to JavaScript objects. The reason for this is that JavaScript objects are only valid in one context, and will likely cause a crash when accessed from the wrong context or from a different thread than the one on which they were created.

This could explain why the worker threads tests are failing. So I'll close this and take another crack at it.