Support classless construct

Description of proposed feature

It would be nice if the manim commands supports construct functions with a surrounding class, similar to how the manimator does it on discord.

from manim import *

def construct(self: Scene) -> None:
    self.add(Circle())

How can the new feature be used?

1. Makes it easier to set up small scenes.
2. Makes it easier to use snippets that were shared on discord.

Additional comments

The manimator also supports omitting the

from manim import *

but I haven't decided on whether I would like to see support of that too.