`BlockingSerialExecutor` Improvements and Extension

[ata-nas]

Story Form

As a Block Node Developer
I want to have an ExecutorService that I can utilize for testing purposes
So that I can test async production logic in a non-flaky way

Technical Notes

DEPENDS ON: #1039

• Files Historic Plugin Unit Tests Pt. 5 #1039 introduces a BlockingSerialExecutor class that is used to make some non-flaky unit tests
• based on this comment thread we should extend the invoke methods with additional functionality that we can actually utilize
• based on this comment thread we can introduce an additional improvement/extension where we will actually run the logic async but joining in order to ensure we can assert logic.
• essentially this implementation would be our "go-to" implementation for testing purposes
• are there any other improvements we can introduce?