chore (Regression Test)[CJS-3815]: Add tests for passing in a custom condition evaluator (#389)

## Summary
#288 introduced an exploratory new feature, the ability to pass custom condition evaluators to the SDK constructor via the option `UNSTABLE_conditionEvaluators`.

The AudienceEvaluator (and its tests) were refactored as a part of that PR, but no tests were added to assert that the `UNSTABLE_conditionEvaluators` worked when passed.

This PR introduces tests to ensure that functionality continues to work.

## Test plan
Unit tests added to assert that:
- You cannot override the built in `custom_attribute` evaluator
- A passed in custom condition evaluator will evaluate conditions of that type
- That the audience condition, user attributes, and logger instance are all passed to the custom evaluator

## Issues
- CJS-3815

Author: James Fox