feat: check non-exists attrs

[Randomizez]

• sanity_check will fail if attrs annotation given but not actually set. e.g.
• Optinal type hint will be ignored

class A(Config):
  a: str

A().sanity_check() # raise AttributeError

class B(Config):
  b: Optional[str]

B().sanity_check() # OK

• warn if use Config(a=a)