feat(models): add shared HTTP client, SSE parser, and stub helpers for Go model drivers (#15821)

### What problem does this PR solve?

The Go model-driver layer () has ~38,700 lines across 109 files. Roughly
74% of that is boilerplate duplicated into every driver: identical HTTP
client setup, the same 65-line SSE scanner loop, and 10-11 one-line "not
supported" stub methods per driver. Any fix must be manually propagated
to every file. Closes #15820.

This PR establishes the three shared utility files that form the
foundation for incremental driver migration:

---

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Refactoring

---------

Co-authored-by: Haruko386 <tryeverypossible@163.com>

internal/entity/models/astraflow.go

@@ -17,7 +17,6 @@
 package models
 
 import (
-	"bufio"
 	"bytes"
 	"context"
 	"encoding/json"
@@ -25,7 +24,6 @@ import (
 	"io"
 	"net/http"
 	"strings"
-	"time"
 )
 
 // AstraflowModel implements ModelDriver for Astraflow (UCloud
@@ -51,20 +49,11 @@ type AstraflowModel struct {
 
 // NewAstraflowModel creates a new Astraflow model instance.
 func NewAstraflowModel(baseURL map[string]string, urlSuffix URLSuffix) *AstraflowModel {
-	transport := http.DefaultTransport.(*http.Transport).Clone()
-	transport.MaxIdleConns = 100
-	transport.MaxIdleConnsPerHost = 10
-	transport.IdleConnTimeout = 90 * time.Second
-	transport.DisableCompression = false
-	transport.ResponseHeaderTimeout = 60 * time.Second
-
 	return &AstraflowModel{
 		baseModel: BaseModel{
-			BaseURL:   baseURL,
-			URLSuffix: urlSuffix,
-			httpClient: &http.Client{
-				Transport: transport,
-			},
+			BaseURL:    baseURL,
+			URLSuffix:  urlSuffix,
+			httpClient: NewDriverHTTPClient(),
 		},
 	}
 }
@@ -264,35 +253,19 @@ func (a *AstraflowModel) ChatStreamlyWithSender(modelName string, messages []Mes
 		return fmt.Errorf("API request failed with status %d: %s", resp.StatusCode, string(body))
 	}
 
-	scanner := bufio.NewScanner(resp.Body)
-	scanner.Buffer(make([]byte, 64*1024), 1024*1024)
 	sawTerminal := false
-	for scanner.Scan() {
-		line := scanner.Text()
-		if !strings.HasPrefix(line, "data:") {
-			continue
-		}
-		data := strings.TrimSpace(line[5:])
-		if data == "[DONE]" {
-			sawTerminal = true
-			break
-		}
-
-		var event map[string]interface{}
-		if err = json.Unmarshal([]byte(data), &event); err != nil {
-			return fmt.Errorf("astraflow: invalid SSE event: %w", err)
-		}
+	done, err := ParseSSEStream[map[string]interface{}](resp.Body, func(event map[string]interface{}) error {
 		if apiErr, ok := event["error"]; ok {
 			return fmt.Errorf("astraflow: upstream stream error: %v", apiErr)
 		}
 
 		choices, ok := event["choices"].([]interface{})
 		if !ok || len(choices) == 0 {
-			continue
+			return nil
 		}
 		firstChoice, ok := choices[0].(map[string]interface{})
 		if !ok {
-			continue
+			return nil
 		}
 		if delta, ok := firstChoice["delta"].(map[string]interface{}); ok {
 			if r, ok := delta["reasoning_content"].(string); ok && r != "" {
@@ -310,14 +283,13 @@ func (a *AstraflowModel) ChatStreamlyWithSender(modelName string, messages []Mes
 		}
 		if finish, ok := firstChoice["finish_reason"].(string); ok && finish != "" {
 			sawTerminal = true
-			break
 		}
-	}
-
-	if err := scanner.Err(); err != nil {
+		return nil
+	})
+	if err != nil {
 		return fmt.Errorf("failed to scan response body: %w", err)
 	}
-	if !sawTerminal {
+	if !done && !sawTerminal {
 		return fmt.Errorf("astraflow: stream ended before [DONE] or finish_reason")
 	}