Compiling to backend

The Qadence 2 internals rely on a few function calls to go from expressions to backend execution. On Qadence 2 platforms, the function responsible for this is compile_to_backend. It creates the bridge between Qadence 2 IR model data and the correct backend defined by the user (or by the compiler). When the user chooses the backend name on Qadence 2 (qadence2-core) at the code_compile function, this information is passed to compile_to_backend to look for the correct backend (using module_importer logic) and, if it exists, backend's compile_to_backend function will be invoked, generating an Interface instance.