Add maze runner tests for feature flags in node

[imjoehaines]

Goal

Adds some maze runner tests for feature flags to the Node test suite. These focus on the request-scoped client having separate lists of feature flags (so each request can have their own set of flags), while also ensuring global flags are supported

[github-actions]

@bugsnag/browser bundle size diff

	Minified	Minfied + Gzipped
Before	42.81 kB	13.06 kB
After	42.81 kB	13.06 kB
±	No change	No change

code coverage diff

Coverage values did not change👌.

Total:

Lines	Branches	Functions	Statements
0%(+0%)	0%(+0%)	0%(+0%)	0%(+0%)

Generated by 🚫 dangerJS against 736cd39

[Cawllec]

LGTM