The noSignalHandler compile-time guard rejects any build of the ffi
modules that doesn't set -d:noSignalHandler (embedded) or
-d:ffiAllowSignalHandler (standalone). test.yml compiled the unit tests
with a raw `nim c` missing the flag, so every per-test job failed at the
guard. The nimble test tasks already pass it; mirror that here.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>