ChannelCacheUnit constructor Null safety

1. sendbird_sdk
2. memory_cache_service
3. ChannelCacheUnit
4. ChannelCacheUnit constructor

ChannelCacheUnit class

1. Constructors
2. ChannelCacheUnit
3. Properties
4. cachedMetaData
5. channel
6. deliveryStatus
7. hashCode
8. readStatus
9. runtimeType
10. typingStatus
11. Methods
12. delete
13. find
14. insert
15. markAsDirty
16. noSuchMethod
17. toString
18. Operators
19. operator ==