Clean render return type

[davep]

This PR tweaks the type hinting for the render methods of various widgets, to ensure they follow the same hinting as is used in our documentation; the aim being to make the code a little less surprising to the reader and also to ensure that any type hint information shown in an IDE, or auto-completed when inheriting from a Textual widget and overriding the render method, matches what would be expected.

Fixes #4063.

[rodrigogiraoserrao]

Looking at this “simple” PR, I can't help but feel like you spent a lot of time making sure you were getting all of the instances and to make sure you don't mix the app and Rich's RenderResult 😬

[rodrigogiraoserrao]

Why are these two imports separated from the other rich.console imports?
Why not the suggestion I show below?

from rich.console import (
    Console,
    ConsoleOptions,
    ConsoleRenderable,
    JustifyMethod,
    RenderableType,
    RenderResult as RichRenderResult,
    RichCast,
)

[davep]

I'll let you have that argument with black and/or whatever else it is that rewrote my code from that.

[rodrigogiraoserrao]

Ah ok, I understand 🤣

[davep]

Looking at this “simple” PR, I can't help but feel like you spent a lot of time making sure you were getting all of the instances and to make sure you don't mix the app and Rich's RenderResult 😬

Yup, that was fun. As I worked through this too I also got to thinking that, in retrospect, it might have been nicer if RenderResult and ComposeResult originated in textual.types too. Possibly. Maybe. Perhaps.