Support in Apex Tests

[Mateusz7410]

Async Lib should allow more support in Apex Tests, such as:

1. Mocking of the executions (synchronously or async)
2. Setting the job to run in synchronous mode (allowing to run chained jobs without running into Test limits).
3. Add Test coverage

[Mateusz7410]

Update:
Since, when using Finalizer, Queueable jobs can enqueue other via Finalizer, with Async lib approach it is possible to get all the results from all the chained jobs, without running into limits.

Because of it, we will focus mostly on the mocking and test coverage here.