Fixes style and mypy

Author: sobolevn

Diff for: returns/either.pyi

@@ -10,7 +10,7 @@ from returns.primitives.monad import Monad, NewValueType, ValueType
 # There's a wierd bug with mypy when we remove this line and use import:
 _MonadType = TypeVar('_MonadType', bound=Union['Monad', 'Either'])
 
-
+# Regular type var, works correctly:
 _ErrorType = TypeVar('_ErrorType')
 
 
@@ -88,6 +88,7 @@ class Right(Either[ValueType, Any], Monad[ValueType]):
     def failure(self) -> NoReturn:
         ...
 
+
 # Useful aliases for end users:
 
 Result = Either

Diff for: returns/maybe.pyi

@@ -89,5 +89,3 @@ class Some(Maybe[ValueType]):
 
     def failure(self) -> NoReturn:
         ...
-
-reveal_type(Some(1).bind(lambda x: Success('s')).unwrap())

Diff for: returns/primitives/monad.pyi

@@ -3,8 +3,9 @@
 from abc import ABCMeta, abstractmethod
 from typing import Any, Generic, NoReturn, TypeVar
 
-ValueType = TypeVar('ValueType')
-NewValueType = TypeVar('NewValueType')
+# These type variables are widely used in our source code.
+ValueType = TypeVar('ValueType')  # noqa: Y001
+NewValueType = TypeVar('NewValueType')  # noqa: Y001
 
 
 class _BaseMonad(Generic[ValueType], metaclass=ABCMeta):