Run _all_ tests under Miri.

[mcy]

Currently, some tests have #[cfg_attr(miri, ignore)] because they call into ring which calls into some assembly.

The best way to deal with this is probably to mock out all of the ring components to do nothing when #[cfg(miri)] holds.

[xaep]

Hi @mcy , I can take this one.

[mcy]

Assigned! GH failed to notify me of your comment >_>