v2.0: multi-step episodes, procedural bugs, semantic grading, sessions, 71 tests

Fix all things

fix: replace asdict with model_dump in client.py step method

fix: use bug_triage_client to avoid openenv-core client conflict

fix: add MAX_STEPS and rate limit delay to baseline

fix: all OpenEnv models as pure Pydantic, no dataclass

complete bug triage openenv environment