rust-matchers: remove default implementations for `Matcher` trait
We don't expect a whole lot of matchers to be defined, and this makes it more
obvious what a matcher does by reading its `impl Matcher for FooMatcher`.
This patch has the added benefit of fixing the `AlwaysMatcher`, its `matches`
function differs from the former default.
Differential Revision: https://phab.mercurial-scm.org/D7255
This directory is meant to cache artifacts useful for tests (such as bundle).
Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.
The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.