feat: add Media.extend

[JuroOravec]

This PR:

• Makes the Component.media instance to inherit the JS and CSS from parent components
• Users can opt-out or configure the inheritance behaviour with the extend attribute on Component.Media, which behaves similarly to Django's Media.extend.
• Clears up behaviour around subclassing components by documenting it

This addresses points 4. and 5. from this discussion.

Examples:

Normal media inheritance:

class ParentComponent(Component):
    class Media:
        js = ["parent.js"]

class MyComponent(ParentComponent):
    class Media:
        js = ["script.js"]

print(MyComponent.media._js)  # ["script.js", "parent.js"]

Disable media inheritance:

class ParentComponent(Component):
    class Media:
        js = ["parent.js"]

class MyComponent(ParentComponent):
    class Media:
        extend = False  # Don't inherit parent media
        js = ["script.js"]
print(MyComponent.media._js)  # ["script.js"]

Specific set of parent Media classes

In this case, the media files are inherited ONLY
from the specified components, and NOT from the original parent components:

class ParentComponent(Component):
    class Media:
        js = ["parent.js"]

class MyComponent(ParentComponent):
    class Media:
        # Only inherit from these, ignoring the files from the parent
        extend = [OtherComponent1, OtherComponent2]
        js = ["script.js"]

print(MyComponent.media._js)  # ["script.js", "other1.js", "other2.js"]

And some documentation :)

Screen.Recording.2025-01-07.at.20.18.19.mov

[JuroOravec]

Previously, the media instance contained only the JS / CSS files from the current Component class, so it was enough to just instantiate it. Now, the _get_comp_cls_media travels up the Component's parent classes to find all the JS / CSS. And so the child component class end up inheriting them all.

[EmilStenstrom]

This looks awesome. Ready to merge. Really like the tests, simple and effective.

I think I remember you describing that we've implemented Media "except for the extends" somewhere in the docs, but I don't see that removed here?

[JuroOravec]

@EmilStenstrom Yeah that's true, thanks for reminding me that!