title: Are __slots__ defined in stubs (.pyi) or in implemetantion (.py)
body: <p>I'm working on a python package and and I've separated the actual implementation code from all the typing annotation and overrides for a cleaner code, and also when using sphinx's autodocs extension I want my signatures to appear without annotations <em>(types already specified in docstrings)</em>, I'm not exactly sure whether this separation is a good practice or not but MyPy and flake8 doesn't seem to complain. And I'm not sure where exactly to define the <code>__slots__</code>, my best bet was:</p>
  <pre class="lang-py prettyprint-override"><code># package/module.pyi
  
  class MyClass:
     __name: str
     __optional: bool
  </code></pre>
  <p>And</p>
  <pre class="lang-py prettyprint-override"><code># package/module.py
  
  class MyClass:
     __slots__ = '__name', '__optional'
  </code></pre>
  <p>Those that seems right? is there a better approach?</p>