A single failing provider derivative breaks the whole responsive video output

Problem/Motivation

The responsive video builder calls the provider derivative and poster methods directly, so one failing source breaks the rendering of the whole video and the page containing it. With providers now allowed to throw for invalid delivery URLs (#3616656: Invalid provider URLs can reach the rendered video markup), the builder needs per-source failure handling.

Steps to reproduce

1. Configure a responsive video style whose provider throws while building a derivative or poster, for example because of an invalid stored delivery URL.
2. Render the file: the exception escapes the builder and breaks the render.

Proposed resolution

Wrap the per-source derivative and poster building, log failures to a new responsive_video_style logger channel and skip the affected source or variant. The shared local fallback source keeps the video playable; a failed poster renders without a poster.

Remaining tasks

Review and merge the prepared fix.

User interface changes

None

API changes

ResponsiveVideoBuilder gains a logger as constructor dependency; new logger.channel.responsive_video_style service.

Data model changes

None