Fix python client model class hydration issue

[shangyian]

Summary

This fixes an issue where the python client's model classes weren't hydrating as dataclasses, but as dictionaries. For example, the expected type of type(col) here should be Column:

source_node = dj.source("source.node")
[type(col) for col in source_node.columns]

This fixes things by adding a custom serializer from dictionaries to DJ model dataclasses: SerializableMixin. This mixin includes a from_dict method that will examine the structure of the dataclass and recursively convert a dictionary to the dataclass.

Test Plan

• PR has an associated issue: Python client not hydrating items as dataclasses #1220
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

N/A

[netlify]

✅ Deploy Preview for thriving-cassata-78ae72 canceled.

Name	Link
🔨 Latest commit	62a9068
🔍 Latest deploy log	https://app.netlify.com/sites/thriving-cassata-78ae72/deploys/672bb33e1fc0bd000840976d

[agorajek]

Thank you for the quick fix!

[agorajek]

This could be part of _internal module, but no big deal either way.

[shangyian]

Yeah, I originally had it there but it felt like that file got really long. This piece is pretty generic whereas that module is now mostly client models.