Add NEAR AI Cloud provider

[PierreLeGuen]

Summary

• Add a native nearai/ model prefix for NEAR AI Cloud TEE inference.
• Fetch and cache NEAR AI Cloud model metadata from the public catalog for model info and --list-models nearai/.
• Document NEARAI_API_KEY, the nearai alias, and nearai/... model usage.

Implementation Notes

• Routes nearai/<model> through LiteLLM's OpenAI-compatible transport using https://cloud-api.near.ai/v1 and NEARAI_API_KEY.
• Maps max_completion_tokens to max_tokens and strips unsupported OpenAI-only parameters for this provider.
• Adds focused tests for metadata lookup, request rewriting, default selection, and settings compatibility.

Testing

• python -m flake8 aider/nearai.py tests/basic/test_nearai.py aider/models.py aider/onboarding.py
• python -m pytest tests/basic/test_nearai.py tests/basic/test_openrouter.py tests/basic/test_models.py::TestModels::test_model_aliases tests/basic/test_models.py::TestModels::test_configure_model_settings tests/basic/test_onboarding.py::TestOnboarding::test_try_select_default_model_deepseek tests/basic/test_onboarding.py::TestOnboarding::test_try_select_default_model_openai tests/basic/test_main.py::TestMain::test_default_model_selection tests/basic/test_main.py::TestMain::test_api_key_multiple -q
• aider --list-models nearai/ --no-gitignore --no-check-update
• aider --model nearai --api-key nearai=fake-key --exit --yes --no-gitignore --no-check-update

A live completion was not run because it requires a real NEARAI_API_KEY.

[CLAassistant]

All committers have signed the CLA.