Improve TS support for enums

[oscartbeaumont]

If you export an enum from Rust it's possible to provide values for multiple variants on the frontend due to the fact that | is typescript is not exclusive or.

I don't think this is a problem with adjacently tagged enums.

This article is a good rundown: https://effectivetypescript.com/2021/11/11/optional-never/

Eg. this demo needs to not compile:

const a: /* Specta output */ { a: string } | { b: string } = {
  a: "abc",
  b: "cde"
};

I think we would have Specta generate { a: string; b: never; } | { a: never; b: string; } instead which would cause the appropriate errors.

For personal reference this came up with search.paths in SD.

[JerwuQu]

Just stumbled into this. Would be very nice to have this feature!