fix: context leak in TestChatStream_EarlyCancel

Add defer cancel() so the context is always cancelled, even when the
loop exits early due to an error before reaching 5 events.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/providers/openai_compat/provider_test.go

@@ -637,6 +637,7 @@ func TestChatStream_EarlyCancel(t *testing.T) {
 	p := NewProviderWithOptions("key", server.URL, "", Options{Stream: true})
 
 	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
 	ch, err := p.ChatStream(ctx, []Message{{Role: "user", Content: "hi"}}, nil, "test", nil)
 	if err != nil {
 		t.Fatalf("ChatStream() error = %v", err)