Improve slow unit tests

[terrykong]

76.26s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_generation_with_hf_training
61.13s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_policy_tensor_parallel
46.26s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_weight_update_and_prefix_cache_reset[2]
46.09s call     tests/unit/utils/test_native_checkpoint.py::test_save_and_load_hf_checkpoint
43.37s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_policy_generation
37.42s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_weight_update_and_prefix_cache_reset[1]
32.76s call     tests/unit/models/generation/test_vllm_generation.py::test_vllm_generate_text
20.92s call     tests/unit/models/policy/test_hf_ray_policy.py::test_all_hf_policy_generation_lps_ref_training[True]
13.63s call     tests/unit/utils/test_venvs.py::test_create_local_venv
12.63s call     tests/unit/models/policy/test_hf_ray_policy.py::test_hf_policy_training
12.61s call     tests/unit/models/policy/test_hf_ray_policy.py::test_hf_policy_generation[False]
12.11s call     tests/unit/models/policy/test_hf_ray_policy.py::test_hf_policy_init
6.58s call     tests/unit/environments/test_math_environment.py::test_math_env_step_basic
5.43s setup    tests/unit/algorithms/test_grpo.py::test_calculate_rewards_single_task
3.96s teardown tests/unit/utils/test_venvs.py::test_create_local_venv
2.72s setup    tests/unit/models/generation/test_vllm_generation.py::test_vllm_policy_generation
2.49s call     tests/unit/data/test_llm_message_utils.py::test_get_formatted_message_log_qwen
2.23s call     tests/unit/data/test_llm_message_utils.py::test_get_formatted_message_log_llama

[terrykong]

test time is now untenable. with the latest dtensor PR we're about 30min in the CI for just unit. will work on a refactor of our unit tests

[parthchadha]

@terrykong closing this issue since we have now switched to a smaller model in our testing.