Add support for dynamic model providers

Implements functionality to parse model names with provider information in the format "provider://model" This allows dynamic provider selection rather than relying only on predefined mappings.

The change affects all execution methods to properly handle these dynamic model specifications while maintaining compatibility with the existing approach for standard model names.

internal/translator/openai/openai/chat-completions/openai_openai_request.go

@@ -4,6 +4,7 @@ package chat_completions
 
 import (
 	"bytes"
+	"github.com/tidwall/sjson"
 )
 
 // ConvertOpenAIRequestToOpenAI converts an OpenAI Chat Completions request (raw JSON)
@@ -17,5 +18,14 @@ import (
 // Returns:
 //   - []byte: The transformed request data in Gemini CLI API format
 func ConvertOpenAIRequestToOpenAI(modelName string, inputRawJSON []byte, _ bool) []byte {
-	return bytes.Clone(inputRawJSON)
+	// Update the "model" field in the JSON payload with the provided modelName
+	// The sjson.SetBytes function returns a new byte slice with the updated JSON.
+	updatedJSON, err := sjson.SetBytes(inputRawJSON, "model", modelName)
+	if err != nil {
+		// If there's an error, return the original JSON or handle the error appropriately.
+		// For now, we'll return the original, but in a real scenario, logging or a more robust error
+		// handling mechanism would be needed.
+		return bytes.Clone(inputRawJSON)
+	}
+	return updatedJSON
 }