Fix Asc and CriticalSection errors, Task.FromResult typing and Shell timeouts

Correct four problems affecting error handling, typed task creation and timeout reporting:

• Calling Asc() with an incomplete UTF-16 surrogate can stop execution even inside Try/Catch. Invalid input should raise a catchable Objo exception.
• The documented Task.FromResult("hello") example cannot be assigned to Task(Of String). The factory should preserve the result's compile-time type.
• Calling CriticalSection.Leave() without a matching successful acquisition can stop execution instead of raising a catchable Objo exception.
• After Shell.Execute() times out, TimedOut incorrectly remains False. It should be True, including when inspected inside the ShellException handler.