refractor(Pipeline): Tiny refractor of code. (#111)

* ref: Refractored pipeline building.

* fix(Tests)

Co-authored-by: Mark Aron Szulyovszky <mark.szulyovszky@gmail.com>

tests/test_walk_forward.py

@@ -35,6 +35,8 @@ class IncrementingStubModel(Model):
 
     data_scaling = "unscaled"
     only_column = None
+    predict_window_size = 'single_timestamp'
+
 
     def __init__(self, window_length) -> None:
         super().__init__()