Clarify difference between copy.copy() and the copy() methods

[serhiy-storchaka]

The copy module documentation mention dict.copy() and list slicing as yet one way of making slice copies. This is true, but there is a subtle difference. dict.copy() returns the instance of dict when copying an instance of the dict subclass, unless it overrides the copy() method. The same for slicing.

Linked PRs

• gh-150636: Clarify difference between copy.copy() and the copy() methods #150637
• [3.15] gh-150636: Clarify difference between copy.copy() and the copy() methods (GH-150637) #150665
• [3.14] gh-150636: Clarify difference between copy.copy() and the copy() methods (GH-150637) #150666
• [3.13] gh-150636: Clarify difference between copy.copy() and the copy() methods (GH-150637) #150667