feat(llm): add Cheaper Inference as a named OpenAI-compatible gateway

[aiapienthusiast]

Summary

• This PR adds Cheaper Inference as a named OpenAI-compatible gateway for LLM clipping.
• It uses the same pattern as feat(llm): add OrcaRouter as a named OpenAI-compatible gateway #205 (OrcaRouter) and Add Atlas Cloud LLM option #181 (Atlas Cloud).
• Cheaper Inference is an OpenAI-compatible LLM gateway. One API key gives access to models from several labs.
• Select a cheaperinference/ model in LLM Model Name, paste the key in APIKEY, and click 'LLM Inference'.
• CHEAPER_INFERENCE_API_KEY and optional CHEAPER_INFERENCE_API_BASE also work.

User impact

Users with a Cheaper Inference key can run LLM clipping without code changes.
FunClip removes the cheaperinference/ prefix and sends the bare model id, like atlascloud/ and minimax/.
Other providers do not change.

Details

Files:

• funclip/llm/openai_api.py: base URL, prefix, and env key in _resolve_model_config.
• funclip/launch.py: prefix list, openai_call route, and 4 dropdown models.
• README.md, README_zh.md: short optional section after OrcaRouter.
• tests/test_cheaperinference_api.py, tests/test_cheaperinference_launch_integration.py: same cases as the OrcaRouter tests.

Live check: gpt-5.4-mini returned a reply through openai_call(..., "cheaperinference/gpt-5.4-mini", ...).

Validation

• I ran the relevant tests or commands:
  • python -m pytest -q tests/test_github_templates.py tests/test_funasr_requirement.py tests/test_installation_docs.py tests/test_openai_api.py tests/test_cheaperinference_api.py tests/test_cheaperinference_launch_integration.py tests/test_orcarouter_api.py tests/test_orcarouter_launch_integration.py tests/test_minimax_api.py tests/test_minimax_launch_integration.py: 40 passed
  • python -m pytest -q tests/test_gradio_runtime_compat.py tests/test_installation_docs.py tests/test_cli_stage_help.py (gradio 4.44.1): 14 passed
  • python3 -m py_compile funclip/launch.py funclip/videoclipper.py funclip/utils/subtitle_utils.py: pass
  • git diff --check: clean
• I checked the affected README/docs links, if changed.
• I verified the affected UI, API, ASR, LLM, or clipping path, if changed.

Screenshots or clips

No screenshots. The UI change adds 4 entries to the existing LLM model dropdown. I tested the LLM call path, not a full video clip.

Notes for reviewers

Dropdown models: gpt-5.4-mini, gpt-5.4, claude-sonnet-5, deepseek-v4-flash. Other model ids also work with the cheaperinference/ prefix.