More precisely determine Impl specialization

[l2dy]

We need to determine if other is a specialization of victim to fix false positive errors of incompatible types.

In commit c8aa7c7, we compare the return type of each Impl members to determine if they are compatible, but it does not cover other cases of incompatibility.

[nev3rfail]

Maybe we can leverage rust-analyzer to do it for us somehow? I don't think doing stuff like this on your own is reasonable because the bigger the code the harder it will get to maintain.

But I do not have enough knowledge about rust-analyzer / lsps to answer it, so its just a thought.