Create guide.merge method on the base class

Author: has2k1

plotnine/guides/guide.py

@@ -156,6 +156,12 @@ def train(
         Returns guide if training is successful
         """
 
+    def merge(self, other: Self) -> Self:
+        """
+        Merge with another guide
+        """
+        return self
+
     def draw(self) -> PackerBase:
         """
         Draw guide

plotnine/guides/guide_colorbar.py

@@ -123,12 +123,6 @@ def train(self, scale: scale, aesthetic=None):
         self.hash = hashlib.sha256(info.encode("utf-8")).hexdigest()
         return self
 
-    def merge(self, other):
-        """
-        Simply discards the other guide
-        """
-        return self
-
     def create_geoms(self):
         """
         Return self if colorbar will be drawn and None if not