Reflection-based ROS2 parser now only returns single component

[oxkitsune]

Related

• Related to RR-2552 (Reflection-based protobuf parser only returns single component #11459)
• Closes RR-2553

What

This changes our ros2_reflection parser to put the entire message behind a single component to make it easier to extract it from lenses.

[github-actions]

Web viewer built successfully.

Result	Commit	Link	Manifest
✅	55adc97	https://rerun.io/viewer/pr/11480	+nightly +main

^{Note: This comment is updated whenever you push a commit.}

[Copilot]

Pull Request Overview

This PR modifies the ROS2 reflection-based parser to consolidate all message fields under a single component named "message" instead of creating separate components for each field, making it easier to extract complete messages from lenses.

• Replaced individual field components with a single "message" component containing a struct
• Removed the empty message handling logic and associated helper function
• Updated the parser to use a single FixedSizeListBuilder with MessageStructBuilder

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
crates/utils/re_mcap/src/layers/ros2_reflection.rs	Core parser logic updated to use single component structure
tests/assets/rrd/snippets/howto/load_mcap.rrd	Test asset updated with new binary hash/size
crates/store/re_data_loader/tests/snapshots/test_mcap_loader__tests__ros2.snap	Snapshot updated with new binary hash/size

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[grtlr]

Nice, great to have this in line with protobuf parsing!