Evaluates all executed test case results using the configured graders.
The run must have completed execution first (status executed).

By default (async_mode=true) this returns a V2RunActionResponse
immediately with the run in a non-terminal state — poll
GET /testing/v2/runs/{run_id} until status is completed, failed, or
cancelled. Set async_mode=false to block until evaluation finishes and
receive the updated V2Run.