feat: add FutureExample demonstrating Future with ExecutorService

WHAT was added:
- A new class `FutureExample` inside `ExecutorsFramework` package.
- Uses `ExecutorService` with `newSingleThreadExecutor()`.
- Submits a lambda task returning `42`.
- Demonstrates:
  - `future.get()` to retrieve result.
  - `future.isDone()` to check task completion.
  - Proper shutdown of ExecutorService.

WHY this matters:
- Introduces `Future` API usage in Java concurrency.
- Shows how to retrieve results of asynchronous tasks.
- Highlights non-blocking task submission + blocking result retrieval.
- Serves as a minimal example for teaching/explaining Future basics.

HOW it works:
1. `executorService.submit(() -> 42)` submits a `Callable<Integer>` task.
2. A `Future<Integer>` is returned immediately (non-blocking).
3. `future.get()` blocks until the task completes and retrieves `42`.
4. `future.isDone()` confirms task completion.
5. `executorService.shutdown()` ensures graceful resource cleanup.

USE CASES:
- Running background tasks where results are required later.
- Asynchronous computation in applications like:
  - API requests
  - Database queries
  - File processing

GOTCHAS:
- `future.get()` is blocking; it waits until task completion.
- If the task throws an exception, `ExecutionException` is wrapped and thrown.
- Must call `shutdown()` to release executor resources.

KEYWORDS:
future executorservice singlethreadexecutor async callable blocking get isDone.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section19MultiThreading/ThreadPooling/src/ExecutorsFramework/FutureExample.java renamed to Section19MultiThreading/ThreadPooling/ExecutorsFramework/src/ExecutorsFramework/FutureExample.java

@@ -17,4 +17,4 @@ public static void main(String[] args) throws ExecutionException, InterruptedExc
         executorService.shutdown();
 
     }
-}
+}