fix: Simplify SubModule exception handling control flow (#1563) (#1701)

- Return result directly instead of going through TaskCompletionSource
- Throw exception directly instead of re-awaiting the TCS
- Use TrySetResult/TrySetException for safety
- Clearer control flow and proper exception propagation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: thomhurst

src/ModularPipelines/Modules/SubModule.cs

@@ -26,17 +26,21 @@ public async Task<T> Execute(Func<Task<T>> action)
             Duration = stopwatch.Elapsed;
             EndTime = DateTimeOffset.UtcNow;
             Status = Status.Successful;
-            SubModuleResultTaskCompletionSource.SetResult(result);
+            SubModuleResultTaskCompletionSource.TrySetResult(result);
+
+            return result;
         }
         catch (Exception ex)
         {
             Duration = stopwatch.Elapsed;
             EndTime = DateTimeOffset.UtcNow;
             Status = Status.Failed;
-            SubModuleResultTaskCompletionSource.SetException(new SubModuleFailedException(this, ex));
-        }
 
-        return await SubModuleResultTaskCompletionSource.Task.ConfigureAwait(false);
+            var wrappedException = new SubModuleFailedException(this, ex);
+            SubModuleResultTaskCompletionSource.TrySetException(wrappedException);
+
+            throw wrappedException;
+        }
     }
 
     public override Task CallbackTask => SubModuleResultTaskCompletionSource.Task;