Refactor code

[hungps]

Currently, the code is a little bit messy, hard to maintain, and scale. I'm working on it and there are some things to do (there will be change if I found somethings is better):

• Use pedantic
• Use riverpod (flutter_riverpod only)
• Add splash screen and init things in here
• Apply clean architecture
• Fetch the pokemon data in gist using dio and json_annotation instead of storing in the app
• Cache the data using hive
• Refactor all widgets

The main work is in the refactor branch and will be merged to the master branch when completed.