Add KDocs for non-deprecated `toList` APIs

# Add KDocs for non-deprecated `toList` APIs

The file `core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toList.kt` has two public, undocumented functions. Please add concise KDocs for both.

### Scope

- `DataFrame.toList()` — converts the frame into a `List`, using the data schema `T` to map each row to an instance.
- `DataFrame<*>.toListOf()` — same, but converts into a `List` for an explicitly provided type `T`, regardless of the frame's own schema.

### KDocs should explain

- What each returns (`List`, one element per row).
- The difference between the two: `toList()` uses the frame's schema type `T`; `toListOf()` takes the target type as an explicit type argument.
- That each row is mapped to a `T` instance by matching column names to `T`'s properties.

### Acceptance criteria

- Both `toList()` and `toListOf()` have concise KDocs.
- The KDocs make the schema-`T` vs explicit-`T` distinction clear.

Start in core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/toList.kt and inspect the two public functions, toList() and toListOf(). Add concise KDocs describing the List result, row-to-property-name mapping, and the distinction between the frame schema type and an explicit target type. Done means both functions are documented and the project’s documentation or test checks pass.

Written by the indexing model from the issue text.