simplify teal data usage in teal

[donyunardi]

Summary

Motivated by this issue, the team believes there's an opportunity to make teal.data a lot simpler by removing the TealDataset class.

Tasks

• Create a rough prototype (currently being done in Prototype ddl + tdata teal.data#140)
• Review and discuss prototype with team
• If agreed, discuss Implementation plan

Related issues

These are issues that were ongoing and set the stage for this roadmap card. It is possible that we will not be merging the the PR related to these issues but this information is useful as reference.

• Output of TealData should be tdata teal.data#121
• Use tdata inside teal::init teal#783

[donyunardi]

Closing in favor of #41