Use the HVM AST for representing inets inside the compiler

[developedby]

Currently we use a gutted version of hvm-core's AST and copied over the transformations we needed.
We should complete the move to using hvm's AST instead, by adding it as a dependency, which will slightly simplify things.

It will also allow us to implement compile-time reduction since we'll get the execution semantics and evaluation for free if we use the hvm crate.