3d removal of background

https://www.notion.so/qim-dtu/3D-remove-background-function-fac8e64da886429eacd9520bc7be0610?pvs=4

implemented into existing filters framework

qim3d/processing/filters.py

@@ -223,12 +223,12 @@ def tophat(vol, **kwargs):
     Remove background from the volume
     Args:
         vol: The volume to remove background from
-        radius: The radius of the structuring element (default: 1)
+        radius: The radius of the structuring element (default: 3)
         background: color of the background, 'dark' or 'bright' (default: 'dark'). If 'bright', volume will be inverted.
     Returns:
         vol: The volume with background removed
     """
-    radius = kwargs["radius"] if "radius" in kwargs else 1
+    radius = kwargs["radius"] if "radius" in kwargs else 3
     background = kwargs["background"] if "background" in kwargs else "dark"
     
     if background == "bright":