[openai] Include ResponseInfo in response (#571)

## Summary
Populates `ResponseInfo` in the response object for openai calls.

## How was it tested?
CICD

## Community Contribution License

All community contributions in this pull request are licensed to the
project maintainers under the terms of the [Apache 2
License](https://www.apache.org/licenses/LICENSE-2.0).

By creating this pull request I represent that I have the right to
license the contributions to the project maintainers under the Apache 2
License as stated in the [Community Contribution
License](https://github.com/jetify-com/opensource/blob/main/CONTRIBUTING.md#community-contribution-license).

Author: ipince

aisdk/ai/provider/openai/internal/codec/decode.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strings"
+	"time"
 
 	"github.com/openai/openai-go/v2/responses"
 	"go.jetify.com/ai/api"
@@ -31,6 +32,11 @@ func DecodeResponse(msg *responses.Response) (*api.Response, error) {
 
 	// Create the response with the extracted fields
 	resp := &api.Response{
+		ResponseInfo: &api.ResponseInfo{
+			ID:        msg.ID,
+			ModelID:   msg.Model,
+			Timestamp: time.Unix(int64(msg.CreatedAt), 0).UTC(),
+		},
 		Content:          content.Content,
 		Usage:            decodeUsage(msg.Usage),
 		ProviderMetadata: decodeProviderMetadata(msg),

aisdk/ai/provider/openai/internal/codec/decode_test.go

@@ -3,6 +3,7 @@ package codec
 import (
 	"encoding/json"
 	"testing"
+	"time"
 
 	"github.com/openai/openai-go/v2/responses"
 	"github.com/stretchr/testify/assert"
@@ -20,6 +21,9 @@ func TestDecodeResponse(t *testing.T) {
 		{
 			name: "simple message",
 			input: `{
+				"id": "resp_123",
+				"created_at": 1741269019,
+				"model": "gpt-4",
 				"output": [
 					{
 						"type": "message",
@@ -37,6 +41,11 @@ func TestDecodeResponse(t *testing.T) {
 				}
 			}`,
 			want: &api.Response{
+				ResponseInfo: &api.ResponseInfo{
+					ID:        "resp_123",
+					ModelID:   "gpt-4",
+					Timestamp: time.Date(2025, 3, 6, 13, 50, 19, 0, time.UTC),
+				},
 				Content: []api.ContentBlock{
 					&api.TextBlock{Text: "Hello world"},
 				},