Add data-plane support in the typespec authoring skill

[catalinaperalta]

This PR includes:

• Updates to the skill for data-plane support
• Initial data-plane support test cases

[github-actions]

📊 GEPA Skill Quality Scores

Skill	Quality	Triggers	Tests
azsdk-common-generate-sdk-locally	❌ 0.30	N/A	---
azsdk-common-pipeline-troubleshooting	❌ 0.34	N/A	---
azsdk-common-prepare-release-plan	❌ 0.37	N/A	---
azsdk-common-sdk-release	❌ 0.37	N/A	---
markdown-token-optimizer	❌ 0.39	N/A	---
azure-typespec-author	❌ 0.40	N/A	---
azsdk-common-apiview-feedback-resolution	❌ 0.43	N/A	---
skill-authoring	❌ 0.48	N/A	---
sensei	⚠️ 0.57	N/A	---

0/9 skills at quality ≥ 0.80

How to improve

# Score a specific skill
python .github/skills/sensei/scripts/gepa/auto_evaluator.py score --skill <name> --skills-dir .github/skills --tests-dir tests

# Optimize a skill with GEPA
python .github/skills/sensei/scripts/gepa/auto_evaluator.py optimize --skill <name> --skills-dir .github/skills --tests-dir tests