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. disableOfflinePush
8. enableOfflinePush
9. fetchConversationSilentMode
10. fetchPreferredNotificationLanguage
11. fetchPushConfigsFromServer
12. fetchSilentModeForAll
13. fetchSilentModeForConversations
14. getNoPushGroupsFromCache
15. getNoPushUsersFromCache
16. getPushConfigsFromCache
17. noSuchMethod
18. removeConversationSilentMode
19. setConversationSilentMode
20. setPreferredNotificationLanguage
21. setSilentModeForAll
22. toString
23. updateAPNsDeviceToken
24. updateFCMPushToken
25. updateHMSPushToken
26. updatePushDisplayStyle
27. updatePushNickname
28. updatePushServiceForGroup
29. updatePushServiceFroUsers
30. Operators
31. operator ==