Some methods for encoding/decoding are implemented manually

[ushmz]

Is your feature request related to a problem? Please describe.

Some factory methods and extensions are manually implemented, which are used to encode/decode JSON. These can be generate with package and reduce some code.

e.g.

• fromJson(), toJSON() methods.
• Getting Enum value from ID, (and verse vice).

It's not a serious problem, priority is relatively low.

Describe the solution you'd like

Use json_serializable package to simplify code.

Describe alternatives you've considered

For now, necessary methods are manually implemented, so "wontfix" is also good.

Additional context