feat(go-models): migrate batch 1 model drivers to unified handlers (#17696)

## Summary

Relate to #17284

Migrate 10 OpenAI-compatible drivers (`302ai`, `aliyun`, `astraflow`,
`avian`, `azure_openai`, `baichuan`, `baidu`, `cometapi`, `deepinfra`,
`futurmix`) to use the unified response handlers
(`HandleNonStreamingResponse` / `HandleStreamingResponse`), following
the same pattern established by `deepseek` in #17634.

- Cut ~150 lines per driver (1507 lines removed, 144 added across 10
files).
- No functional changes — pure deduplication of HTTP plumbing.
- Each driver now routes through `baseModel.doRequest()` and
`HandleNonStreamingResponse()`.

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/entity/models/cometapi_test.go

@@ -801,7 +801,7 @@ func TestCometAPIEmbedRejectsHTTPError(t *testing.T) {
 	apiKey := "test-key"
 	model := "text-embedding-3-small"
 	_, err := m.Embed(ctx, &model, []string{"a"}, &APIConfig{ApiKey: &apiKey}, nil, nil)
-	if err == nil || !strings.Contains(err.Error(), "CometAPI embeddings API error") {
-		t.Errorf("expected CometAPI embeddings API error, got %v", err)
+	if err == nil || !strings.Contains(err.Error(), "status 401") {
+		t.Errorf("expected embeddings API error for HTTP 401, got %v", err)
 	}
 }