fix: replace chat_completion by chat.completion in providers responses

[unsync]

Author Description

Title:
Some providers had the wrong value for the object field, not a major issue but this replacement makes their responses fully openai compatible.

Title: fix: replace chat_completion by chat.completion in providers responses

🔄 What Changed

• Updated the object field value from chat_completion to chat.completion in response transformation functions
• Affected 8 provider files with minimal changes

🔍 Impact of the Change

• Makes provider responses fully OpenAI compatible
• Ensures consistent response format across all providers
• Improves API compatibility for consumers of the gateway

📁 Total Files Changed

• 8 files modified with 9 additions and 9 deletions
• All changes are consistent string replacements

🧪 Test Added

• N/A

🔒 Security Vulnerabilities

• N/A

Quality Recommendations

1. Consider adding a simple test case to verify the response format compatibility with OpenAI

2. Add a comment explaining why 'chat.completion' is the correct format for OpenAI compatibility