BF: Fix attempting to delete frame local symbol table variable

Fix attempting to delete frame local symbol table variable: starting
Python 3.13 attempting to delete local variables is not allowed.

Fixes:
```
>       del values['self']
E       TypeError: cannot remove variables from FrameLocalsProxy

../../BUILDROOT/usr/lib64/python3.13/site-packages/dipy/workflows/multi_io.py:177: TypeError
```

Documentation:
https://docs.python.org/3.13/whatsnew/3.13.html#defined-mutation-semantics-for-locals
https://peps.python.org/pep-0667/

dipy/workflows/multi_io.py

@@ -175,9 +175,18 @@ def io_iterator_(frame, fnc, output_strategy="absolute", mix_names=False):
         Properly instantiated IOIterator object.
 
     """
+
+    # Create a new object that does not contain the ``self`` dict item
+    def _selfless_dict(_values):
+        return {key: val for key, val in _values.items() if key != "self"}
+
     args, _, _, values = inspect.getargvalues(frame)
     args.remove("self")
-    del values["self"]
+    # Create a new object that does not contain the ``self`` dict item from the
+    # provided copy of the local symbol table returned by ``getargvalues``.
+    # Avoids attempting to remove it from the object returned by
+    # ``getargvalues``.
+    values = _selfless_dict(values)
 
     spargs, defaults = get_args_default(fnc)