Use version marker trait for ISL model

[desaikd]

Current APIs for creating an ISL model allows mixing different versioned ISL constraints. When we try to resolve this ISL model by loading the schema(load_schema()) it returns error if the constraints are from different ISL versions. If we have something that returns a compile-time error while constructing the ISL model that gives an ease of use for the API.

We can create a marker trait for ISL versioning and have it implement for different ISL versions.
e.g.

trait IslVersion {} // ISL version marker trait

struct IslV1_0 {}
struct IslV2_0 {}

This can be used to define ISL model structs over the generic marker trait IslVersion. We can then have a particular version struct implementation for a constraint. This allows us to define constraints based on its version and gives a compile time error when a constraint doesn't exist for the given ISL version.