When building a tree or opening a writer, we don't check if the distances matches

[irevoire]

Currently, I can open a Writer with the wrong distance type, and it works, it shouldn’t.

IMO, in terms of API, it’s the new that should return an error if the metadata exists and doesn't contain the right distance type.
But at the same time, opening database should be super quick, so maybe it should be in the build.
We need to think about it.