feat: Add callback_barycenter parameter to FUGWSparseBarycenter class

src/fugw/mappings/sparse_barycenter.py

@@ -156,6 +156,7 @@ def fit(
         mesh_sample=None,
         nits_barycenter=5,
         device="auto",
+        callback_barycenter=None,
         verbose=False,
     ):
         """Compute barycentric features and geometry
@@ -192,6 +193,11 @@ def fit(
         device: "auto" or torch.device
             if "auto": use first available gpu if it's available,
             cpu otherwise.
+        callback_barycenter: callable or None
+            Callback function called at the end of each barycenter step.
+            It will be called with the following arguments:
+
+                - locals (dictionary containing all local variables)
 
         Returns
         -------
@@ -274,6 +280,9 @@ def fit(
                 plans, weights_list, features_list, device
             )
 
+            if callback_barycenter is not None:
+                callback_barycenter(locals())
+
         return (
             barycenter_weights,
             barycenter_features,