toDataFrame loses types of properties with type parameter return type

easy repro with unfold Pair<Int, String>, toDataFrame under the hood:
`dataFrameOf("a" to columnOf(1 to "str")).unfold { a }`

Actual:
```
a:
 first: Any
 second: Any
```

Expected:
```
a:
 first: Int
 second: String
```