This PR refactors properties that contain only a single return statement by converting them to expression-bodied members, reducing boilerplate and improving readability.
- Getters and setters with a single statement in their bodies can be simplified: The `IsDone` property originally used a full getter block to evaluate whether all coroutine handles are inactive. We replaced it with an expression-bodied property (`public bool IsDone => _handles.All(handle => !_scheduler.IsCoroutineAlive(handle));`) and relocated the explanatory comment above it, streamlining the code.
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