Refactor remove_background function to use specified median filter size and update tophat filter

qim3d/processing/__init__.py

+from .detection import *
 from .filters import *
 from .local_thickness import local_thickness
+from .operations import *
 from .structure_tensor import structure_tensor
-from .detection import *

qim3d/processing/operations.py

-import qim3d
 import qim3d.processing.filters as filters
 
 
@@ -17,7 +16,7 @@ def remove_background(vol, **kwargs):
     size = kwargs["size"] if "size" in kwargs else 2
     
     # Create a pipeline with a median filter and a tophat filter
-    pipeline = filter.Pipeline(
+    pipeline = filters.Pipeline(
         filters.Median(size=size),
         filters.Tophat(**kwargs)
     )