Faster cardinality and repr implementation of Set_object_enumerated

[user202729]

Otherwise, you try to print out a Set(GF(998244353)) and it eats all your computer's memory

compare with

sage: repr(matrix.zero(100))
'100 x 100 dense matrix over Integer Ring'
sage: str(matrix.zero(100))[:50]
'[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0'
sage: repr(matrix.zero(3))
'[0 0 0]\n[0 0 0]\n[0 0 0]'
sage: str(matrix.zero(3))
'[0 0 0]\n[0 0 0]\n[0 0 0]'

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[mantepse]

how can o is self happen?

[user202729]

Set_object_binary does Set_object.__init__(self, self, category=category)

many of them override this method, but better safe than sorry.

(seriously it's probably better to not make Set_object_binary inherit from Set_object at all... but I consider that out of scope)