feat(cli): add fine-tuning model limits command

[cursor]

Summary

• add tg fine-tuning model-limits / tg ft model-limits for the generated fine-tuning model limits SDK method
• route existing fine-tuning model limit helper through client.fine_tuning.model_limits
• update CLI fixtures/tests for the generated model-limits response shape

Tests

• .venv/bin/python -m pytest tests/cli/test_fine_tuning.py
• .venv/bin/python -m pytest tests/unit/test_fine_tuning_resources.py
• .venv/bin/python -m ruff check src/together/lib/cli/__init__.py src/together/lib/cli/api/fine_tuning/model_limits.py src/together/lib/resources/fine_tuning.py tests/cli/test_fine_tuning.py
• .venv/bin/python -m ruff format --check src/together/lib/cli/__init__.py src/together/lib/cli/api/fine_tuning/model_limits.py src/together/lib/resources/fine_tuning.py tests/cli/test_fine_tuning.py