Feature: Beta support for /v1/messages route

[narengogi]

trafficstars

TO-DO:

• [ ] model specific additional fields

TO-DO (subsequent versions):

• [ ] support stream concatenation for caching
• [ ] fix types for bedrock

Testing Done:

• [ ] test with claude code
• [ ] test with librechat
• [ ] tool calling
• [ ] thinking
• [ ] multi turn tool calling
• [ ] multi turn thinking
• [ ] redacted thinking