什么是单例模式？
{"response":{"error":"API请求失败","http_code":429,"response":"{\"code\":700002,\"detail\":\"用户请求TPM超限，请减少tokens后重试\",\"message\":\"USER_TPM_RATELIMITING\",\"error\":{\"code\":\"700002\",\"message\":\"用户请求TPM超限，请减少tokens后重试\",\"type\":\"USER_TPM_RATELIMITING\"}}"}}