build: Run miri for mwtitle

miri (https://github.com/rust-lang/miri) is a tool that checks for certain kinds of undefined behavior, especially for unsafe code.

Since mwtitle has some unsafe code, let's try to use miri to audit it.

Unfortunately any test that uses tokio is incompatible with miri because it uses an external syscall (epoll). For now these are ignored but we should see if we can avoid having to invoke requests for these.

Added to the pipeline in rust-ci-pipeline!1 (merged).