Add GeoDataFrame.generate* overloads that generate schema declarations suitable for T : WithGeometry marker parameter

Let's say you read GeoDataFrame.readShapefile and assign schema to it. Right now there's no way to do it without manual editing of generated code

geo.df.generateDataClasses generates a schema without WithGeometry supertype and it's not suitable for our T : WithGeometry bound. So schema has to be edited. Plus, it cannot be applied directly and need geo.modify { it.cast<MySchema>() }

Proposed:

add geo.generateDataClasses() that generates data class MySchema(...) : WithGeometry

and GeoDataFrame.cast

Implementation details:

Generating a schema with specific supertype requires using internal MarkersExtractor to obtain marker for knownMarkers parameter:

val withGeometry = MarkersExtractor.get<WithGeometry>()
val codegen = CodeGenerator.create()
codegen.generate(
    ...,
    knownMarkers = listOf(withGeometry)
)

Start at the GeoDataFrame.generateDataClasses and GeoDataFrame.cast entry points, then trace CodeGenerator.create and MarkersExtractor.get() as described in the issue. Compare the existing geo.df.generateDataClasses behavior with the proposed overloads; done means generated schemas satisfy the WithGeometry bound and can be used directly with GeoDataFrame.cast.