doc: Add additional special methods in class template

Mainly used in:
- Datasetes
- Iterators
- Variable and Parameter

docs/source/_templates/autosummary/class.rst

@@ -15,7 +15,7 @@
    ..
       Special methods
 
-{% for item in ('__call__', '__enter__', '__exit__') %}
+{% for item in ('__call__', '__enter__', '__exit__', '__getitem__', '__setitem__', '__len__', '__next__', '__iter__', '__copy__') %}
 {% if item in all_methods %}
    .. automethod:: {{ item }}
 {% endif %}