What should we add?

Now that classical Vars are now in Rust, and we're going to start using them in the rust native circuit representations, we should consider porting this method to Rust. This method is necessary for some transpiler passes to transition into being fully rust-native.

Related work:

• Port classical expressions (Expr) to Rust. #14068
• Oxidize classical expression use in Rust code. #14176
• Oxidize VariableMapper and uses. #14361