Minor Description
Currently, the SystemTime class, which provides system time-related functionalities such as getting the current timestamp 、sleep、and await can be instantiated multiple times.
Howerver, system time is unique，In an application, the time obtained in different places should be consistent, But now the time obtained by using the Java System class to interact with the underlying layer is the same。
So I suggest changing it to a singleton mode， reflect the uniqueness of system time in design