[TypeSpec Authoring][Benchmark] Adopt SDK evaluation pipeline framework

[haolingdong-msft]

Parent epic: #15726

Adopt the SDK evaluation pipeline framework for the TypeSpec authoring benchmark so evaluation runs use the shared/standard SDK eval pipeline infrastructure rather than a bespoke setup.

Scope

• Onboard the TypeSpec authoring benchmark onto the SDK evaluation pipeline framework.
• Align eval execution, result collection, and reporting with the shared framework conventions.
• Reduce custom pipeline glue by reusing the framework's standard building blocks.

Created as a sub-issue of the "[Epic][TypeSpec Authoring][Benchmark] Continuous improvement" epic (#15726).