Handle OpenAI API errors in processChatResult

[viicslen]

This pull request adds improved error handling to the processChatResult method in src/Providers/OpenAI/Responses/HandleChat.php. The main change is to ensure that errors returned from the OpenAI API are detected and reported clearly, making debugging and maintenance easier.

Error handling improvements:

• Added a check for an 'error' key in the $result array, throwing a ProviderException with the error message if present.
• Added a check to ensure the 'output' key exists in the $result array, throwing a ProviderException if it is missing.

[ilvalerione]

the "empty output" is not necessary on error. I don't think it should raise an exception. It could depends by the stop reason for example.

[viicslen]

@ilvalerione As I’m not too familiar with the response structure, I have updated the checks to include only what is necessary for the existing array_filter($result['output'], ...) to work. This prevents a TypeError from being thrown when the first parameter is null instead of an array, which is currently happening in some instances.

Alternatively, would it be better to use the null coalescing operator ($result['output'] ?? []) instead?