feat: ros2 lyrical extension (core26)

[florcabral]

Adds support for ROS 2 Lyrical on core26, following the same pattern as the existing ROS 2 Humble (core22) and Jazzy (core24) extensions.

Changes include:

• New extension files: ros2_lyrical.py, ros2_lyrical_desktop.py, ros2_lyrical_ros_base.py, ros2_lyrical_ros_core.py, and _ros2_lyrical_meta.py
• Registered the new extensions in registry.py
• Added core26 support to the colcon plugin (_ros.py)
• Unit tests for the new extensions and updated test_list_extensions.py
• Spread tests for integration testing on core26
• Documentation updates for the how-to guide and reference pages covering the new extensions and base

The extension is currently marked as experimental.

---

• I've followed the contribution guidelines.
• I've signed the CLA.
• I've successfully run make lint && make test.
• I've added or updated any relevant documentation.
• I've updated the relevant release notes.

[mr-cal]

High-level, this looks good. Let me know when this is out of draft and you're ready for an in-depth review.

[mr-cal]

Canonical's copyright policy is:

Add (and keep) the year of first publication. However, it's not necessary to update the year range every year.

I have an email from Canonical's legal team, if you'd like the original reference.

So either don't change the copyrights or do:

Suggested change

	# Copyright 2026 Canonical Ltd.
	# Copyright 2018-2022,2026 Canonical Ltd.