A minimal implementation of Rust's Result type. Used for contract methods that return Results, to maintain their distinction from methods that simply either return a value or throw.

Why is this needed?

This is used by ContractSpec and AssembledTransaction when parsing values return by contracts.

Contract methods can be implemented to return simple values, in which case they can also throw errors. This matches JavaScript's most idiomatic workflow, using try...catch blocks.

But Rust also gives the flexibility of returning Result types. And Soroban contracts further support this with the #[contracterror] macro. Should JavaScript calls to such methods ignore all of that, and just flatten this extra info down to the same try...catch flow as other methods? We're not sure.

For now, we've added this minimal implementation of Rust's Result logic, which exports the Result interface and its associated implementations, Ok and Err. This allows ContractSpec and AssembledTransaction to work together to duplicate the contract's Rust logic, always returning Result types for contract methods that are implemented to do so.

In the future, if this feels too un-idiomatic for JavaScript, we can always remove this and flatten all JS calls to try...catch. Easier to remove this logic later than it would be to add it.