tests: remove doctest in narrowspec, it is broken
I think every item here is considered incorrect (if we fix doctest to run it),
so let's just delete it.
Differential Revision: https://phab.mercurial-scm.org/D8279
rust-core: add missing `Debug` traits
Turns out you need them when trying to use `hg-core` as a library. Who knew.
Differential Revision: https://phab.mercurial-scm.org/D8278