ChatPushManager constructor Null safety

1. agora_chat_sdk
2. agora_chat_sdk
3. ChatPushManager
4. ChatPushManager constructor

ChatPushManager class

1. Constructors
2. ChatPushManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. fetchConversationSilentMode
8. fetchPreferredNotificationLanguage
9. fetchPushConfigsFromServer
10. fetchSilentModeForAll
11. fetchSilentModeForConversations
12. getNoPushUsersFromCache
13. getPushConfigsFromCache
14. getPushTemplate
15. noSuchMethod
16. removeConversationSilentMode
17. setConversationSilentMode
18. setPreferredNotificationLanguage
19. setPushTemplate
20. setSilentModeForAll
21. toString
22. updateAPNsDeviceToken
23. updateFCMPushToken
24. updateHMSPushToken
25. updatePushDisplayStyle
26. updatePushNickname
27. updatePushServiceForGroup
28. Operators
29. operator ==