[upstream-sync] Add Novita AI as LLM provider (upstream PR #1781)

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Upstream Change Summary

Type: new-feature
Difficulty: Easy
Recommendation: Adopt

Upstream PR #1781 adds Novita AI as a new LLM provider using the OpenAI-compatible API at https://api.novita.ai/openai/v1. The implementation follows the same pattern as other OpenAI-compatible providers (LiteLLM, vLLM) and supports both text generation and embeddings. Authentication is via NOVITA_API_KEY environment variable or constructor parameter.

This change adds a new variant to the LlmApiType enum in Rust and a corresponding novita.rs client module wired into the generation and embedding client factories.

Upstream References

• PR: feat: add Novita AI as LLM provider cocoindex-io/cocoindex#1781
• Commit: cocoindex-io/cocoindex@3a618c9
• Upstream repo: https://github.com/cocoindex-io/cocoindex

Relevant Upstream Files / Areas

• rust/cocoindex/src/llm/mod.rs → crates/recoco/src/llm/mod.rs (LlmApiType enum, factory wiring)
• rust/cocoindex/src/llm/novita.rs → crates/recoco/src/llm/novita.rs (new client module)

Recoco Considerations

• Affected modules: crates/recoco LLM module (used by function-embed and function-extract-llm)
• Feature-gating: Should be gated behind the same feature flag as other OpenAI-compatible providers (e.g., function-embed or a new llm-novita gate if desired for fine-grained control)
• API surface: LlmApiType enum gains a Novita variant — this is a non-breaking additive change to recoco's public API
• No Python to exclude: The upstream change is entirely in rust/cocoindex/src/llm/
• Environment variable: NOVITA_API_KEY follows established *_API_KEY pattern already used by other providers

Integration Notes

Pattern is identical to LiteLLM/vLLM adapters. Once the novita.rs module is created with the correct base URL (https://api.novita.ai/openai/v1), the main work is:

1. Adding Novita to LlmApiType
2. Wiring it into generation_client_factory and embedding_client_factory in llm/mod.rs
3. Adding appropriate feature gate and dependency (reqwest or existing HTTP client)