Add attached_pic property to avformat consumer

[bmatherly]

This allows applications to add cover art to files

[Copilot]

Pull request overview

Adds support to the avformat consumer for embedding cover art (FFmpeg “attached picture” stream) into output files, and updates the consumer metadata version accordingly.

Changes:

• Bump consumer_avformat metadata version to 6.
• Add a new attached_pic consumer parameter (file picker) to specify a cover-art image path.
• Implement image loading, basic JPEG/PNG detection, dimension parsing, stream creation, and writing the attached picture packet right after the container header.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/modules/avformat/consumer_avformat.yml	Adds the attached_pic parameter and bumps the module metadata version.
src/modules/avformat/consumer_avformat.c	Implements attached-picture stream creation and writes cover art immediately after the container header.

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[Copilot]

Pull request overview

Adds a new attached_pic consumer property to the avformat (FFmpeg output) module so callers can embed cover art into output files.

Changes:

• Bump avformat consumer definition version and introduce a new attached_pic parameter in the YAML schema.
• Add cover-art handling in consumer_avformat.c: detect JPEG/PNG, parse dimensions, create an attached-picture stream, and write the packet after header (or as Matroska attachment).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/modules/avformat/consumer_avformat.yml	Bumps consumer version and documents the new attached_pic parameter.
src/modules/avformat/consumer_avformat.c	Implements reading an image file and muxing it as cover art via an attached-picture stream/attachment.

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