Remove pydantic from DJ client.

[agorajek]

Summary

Remove pydantic from the DJ client to lower the dependency hell for DJ users.

Some pydantic functionality (like validate and simple attributes) are replaced with data classes.

Test Plan

Unit tests for now. Need to do more.

• [x] PR has an associated issue: #1170
• [x] make check passes
• [x] make test shows 100% unit test coverage

Deployment Plan

deploy and profit

[netlify[bot]]

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