fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

main_test.go

@@ -155,7 +155,7 @@ func TestTranscribeHTTP(t *testing.T) {
 			t.Errorf("expected POST, got %s", r.Method)
 		}
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{"text": "hello world"})
+		_ = json.NewEncoder(w).Encode(map[string]string{"text": "hello world"})
 	}))
 	defer ts.Close()
 
@@ -164,7 +164,7 @@ func TestTranscribeHTTP(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != 200 {
 		t.Errorf("status = %d", resp.StatusCode)
 	}