fix(community): improve TogetherAI error handling for chat models

[christian-bromann]

Description

This PR fixes an issue where users attempting to use chat/instruct models with the TogetherAI class would encounter a cryptic error: Cannot read properties of undefined (reading 'choices'). This happened because the TogetherAI API returns different response formats for text completion models vs chat models, and users were unknowingly using the wrong class.

Changes Made:

1. Improved Error Handling: Added proper error handling in the _call method to catch when the API response doesn't match the expected format and provide a helpful error message directing users to use ChatTogetherAI instead.

2. Model Type Detection: Implemented automatic detection of chat/instruct models (based on patterns like "instruct", "chat", "vision", or "turbo" in model names) and added a console warning when users instantiate TogetherAI with these models.

3. Documentation Updates:

   • Added clear warnings and a model compatibility table to the TogetherAI documentation
   • Updated ChatTogetherAI documentation to clarify when to use each class
   • Included examples of which models work with which class

4. Tests: Added unit tests to verify the warning behavior and model type detection.

Example of the fix in action:

Before (confusing error):

const llm = new TogetherAI({
  model: 'meta-llama/Llama-3.2-11B-Vision-Instruct-Turbo',
});
await llm.invoke('Hello'); 
// TypeError: Cannot read properties of undefined (reading 'choices')

After (helpful guidance):

const llm = new TogetherAI({
  model: 'meta-llama/Llama-3.2-11B-Vision-Instruct-Turbo',
});
// Console warning: "Warning: Model 'meta-llama/Llama-3.2-11B-Vision-Instruct-Turbo' appears to be a chat/instruct model. Consider using ChatTogetherAI from @langchain/community/chat_models/togetherai instead."

await llm.invoke('Hello');
// Error: Unexpected response format from Together AI. The model 'meta-llama/Llama-3.2-11B-Vision-Instruct-Turbo' may require the ChatTogetherAI class instead of TogetherAI class.

This slightly improves the developer experience by providing clear guidance on which class to use for different model types.

Fixes #6993

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Latest commit: c912930

The changes in this PR will be included in the next version bump.

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@langchain/community	Patch

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Project	Deployment	Preview	Comments	Updated (UTC)
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