feat(models): add Cheaper Inference OpenAI-compatible model wrapper

[aiapienthusiast]

This PR adds a CheaperInference model wrapper.
It follows the Atlas Cloud wrapper from #1104.

Cheaper Inference is an OpenAI-compatible LLM gateway.
Its base URL is https://api.cheaperinference.com/v1.

Cheaper Inference is one of the fastest-growing AI routers.
Each model costs 15–60% less than the list price of its lab.

Changes

• Add scrapegraphai/models/cheaperinference.py. It is a ChatOpenAI subclass with a fixed base URL.
• Export CheaperInference from scrapegraphai.models.
• Add a cheaperinference entry with two models to models_tokens.py.
• Add tests/test_cheaperinference_model.py.

Testing

• The new tests and the Atlas Cloud tests pass.
• ruff passes. black and isort pass on the new files.

Details

• Base branch: pre/beta.
• Usage: pass a CheaperInference object as model_instance, with model_tokens, in the graph config. This PR does not register the provider in abstract_graph.py. This matches Add Atlas Cloud OpenAI-compatible model wrapper #1104.
• The Test Suite workflow runs a fixed list of test files. This PR does not change the workflow. A maintainer can add tests/test_cheaperinference_model.py to the list.
• black --check reports scrapegraphai/models/__init__.py. The __all__ line is already too long on pre/beta.
• isort --check-only reports scrapegraphai/models/minimax.py. This PR does not change that file.

[github-actions]

🎉 This PR is included in version 2.3.0-beta.1 🎉

The release is available on:

• v2.3.0-beta.1
• GitHub release

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version 2.3.0 🎉

The release is available on:

• v2.3.0
• GitHub release

Your semantic-release bot 📦🚀