[12.x] Improve discarded attribute violation callable typehints

[mosabbirrakib]

This PR improves the typehints for the discarded attribute violation callback by specifying the exact callable signature.

Improved the lazy loading violation callback typehints, this change makes the callable signature more explicit by changing from callable|null to (callable(self, array))|null.

The callback receives:

• The model instance (self)
• An array of discarded attribute keys (array)

This provides better IDE support and makes the expected callback signature clearer to developers.