Output of TealData should be tdata

[nikolas-burkoff]

Should be done with insightsengineering/teal#783

We are aiming to make tdata the universal data object in the teal framework. This issue is to update the teal.data package so that the data coming out of it for teal::init is of type tdata

1. The class definition of tdata should be moved out of teal and into here
2. TealData$pull() should output a tdata object
3. For non DDL data a tdata object should be created from the datasets
4. tdata should have CodeClass

In the future insightsengineering/teal#937 along with insightsengineering/teal#764 (comment) will simplify the teal.data api and push the use of tdata further into teal.data but that is not this issue

[gogonzo]

Probably we need to store CodeClass in tdata as we need a way to subset code for selected datasets. code could be an expression only if we decide to not subset the code or if we figure out this