RFC: Trait expects interface

Hello internals! Since «traits» are often an indicator of not very good code and many may not use them quite correctly, for example, as helpers, I suggest adding support for the expects keyword to indicate that the trait is part of the code decomposition taking into account ISP. For example: ``` // Definition trait LoggerTrait expects LoggerInterface {     // ... } // Usage class MyService {     use LoggerTrait; // Fatal Error: Class MyService expects LoggerInterface to be implemented } class MyService2 implements LoggerInterface {     use LoggerTrait; // OK } ``` How relevant do you think this idea/proposal is? And what possible problems or solutions will this entail in the future?   -- Kirill Nesmeyanov