Valgrind CI pass

The test suite supports running under valgrind if additional flags are passed. Two tests are known to not work (Simo believes this is because they rely on program name matching). So we would need a separate pass.

We would also want to generate a suppressions file for libverto/libev (but this is probably not worth it - these are fixed-size one-time leaks, and valgrind has trouble generating useful traces for it).