create layer package and abstract class

src/layers/__init__.py

@@ -0,0 +1,2 @@
+from .layer import Layer
+from .transcoder import Transcoder

src/layers/layer.py

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+from abc import ABC, abstractmethod
+from dir import Root
+
+class Layer(ABC):
+    def __init__(self):
+        pass
+
+    @abstractmethod
+    def __process(self, root: Root):
+        raise NotImplementedError