- mirror spack-latest.yaml, with -fsanitize=thread on the libzmq and
libsodium nodes so tsan can observe the happens-before edges established
inside libzmq's lock-free queues, plus the libstdcxx-tsan root spec
- flags are applied per node instead of via the propagating '==' operator,
which could reach the gcc node and trigger a compiler rebuild
- unchanged roots (fairlogger, boost, ninja, cmake) keep their spec hashes,
so they are shared with the regular buildcache entries; the instrumented
nodes hash differently and coexist in the content-addressed cache
- exclude libstdcxx-tsan from concretizer reuse so recipe changes always
take effect; unchanged recipes still hit the buildcache because the spec
hash is identical
- add the tsan env to the buildcache matrix (rebuilding also on spack_repo
changes) so the instrumented binaries are cached instead of rebuilt on
every CI run
