Context Values: Replace Pydantic schemas with TypedDicts

[Zaimwa9]

The overarching goal is to get rid of the vendored-in Pydantic models and ultimately the pydantic dependency:

• Replace Pydantic models with types added in Provide a common package to replace Pydantic models flagsmith-common#128.
  • Port DynamoDB validators (Decimals) and helper into the edge-api
• Preserve mapping/validation logic for trait values.
• Make sure the tests pass.