Mirror JCO generated Result type

[nicoburniske]

/** Type representing success or failure. */
export type Result<T, E = unknown> = Result.Ok<T> | Result.Err<E>;

export namespace Result {
    /**
     * The type of a successful result.
     * @example
     * const success: Result.ok<number> = Result.ok(123)
     */
    export type Ok<T> = typeof prototype & {
        readonly value: T;
        readonly error?: never;
        readonly isOk: true;
        readonly isErr: false;
    };

    /**
     * A failed result.
     * @example
     * const failure: Result.err<string> = Result.err('error')
     */
    export type Err<E> = typeof prototype & {
        readonly value?: never;
        readonly error: E;
        readonly isOk: false;
        readonly isErr: true;
    };

value field should always contain the success value, or the error

there should be a field "tag" that is either "ok" or "err" like the type generated by JCO

See here https://github.com/golemcloud/jco/blob/085e0b32eaa91e9b2e1783dc56515f61fc62583f/crates/js-component-bindgen/src/ts_stubgen.rs#L498

export type Result<T, E> = { tag: "ok"; val: T } | { tag: "err"; val: E }

This would make the two result types more consistent. We should also include conversion types between the two if possible

Also need to test if once the change is good, you can just return a golem-ts Result in your wit world exported functions, instead of converting back and forth. would be great if we can support this