Switch `yaml-rust2` to `saphyr`

[LecrisUT]

Afaiu the project is still very early in its split so the API changes should not be that much different for now. At least the tests are passing, but please double-check the changes.

Closes: #654

[epage]

As there isn't a decision on #654, I'm going to move this to a Draft to make the intention clear that this is not yet ready for review.