Compose, don't block

Implement with CompletableFuture (returned before completion, joined by the test): 1. static CompletableFuture<Integer> combined() — two async supplies (return 20 and 22), combined with thenCombine into their sum. 2. static CompletableFuture<Integer> chained() — an async 3, thenCompose to double it, thenApply to add 4 (=> 10). 3. static CompletableFuture<Integer> recovered() — an async that throws, then exceptionally returning -1. 4. static CompletableFuture<Integer> bounded() — async sleeping 50ms then returning 7, with orTimeout(10, MILLISECONDS) and exceptionally returning -1 (timeout path exercised).

Difficulty: advanced