Run validations for the #perform instance method

[naikipl]

The perform instance method does not currently run validations, and it should.

Validations run perfectly for the class method:

MyUseCase.perform

Validations do not run for the instance method:

use_case = MyUseCase.new
use_case.perform

Since the instance method is intended to be overridden by the class that includes UseCasePattern, we can't just add the valid? check into the perform method. We need to figure out a way to do this smartly.