Shows an example how a task can be submitted N times for retries and an await block to ensure all of the tasks are completed.
This example demonstrates a robust retry mechanism for asynchronous task execution, where a task submitted up to three times eventually succeeds after initial failures, with an await block ensuring all tasks complete before results are collected. It shows how `FixedExecutionRunnable` wraps a `Callable` using `ScheduledExecutorService`, `CountDownLatch`, and `ScheduledFuture` to schedule retries at fixed delays, while `DummyCallable` throws exceptions on the first two attempts. The code uses Scala collections like `ListBuffer` and `AtomicInteger` to simulate three concurrent task submissions, verifying the final output matches the expected task names.