custom_shimmer library Null safety

1. weather
2. custom_shimmer library

weather package

1. Libraries
2. animated_background
3. colors
4. custom_card
5. custom_divider
6. custom_image
7. custom_shimmer
8. environment
9. extensions
10. http_connection
11. logger
12. main
13. main_screen
14. model
15. navigations
16. open_weather
17. preferences
18. search_location_screen
19. splash_screen
20. themes
21. utils
22. weather_http
23. weather_provider
24. weather_screen