test: ignore expensive tests by default

This makes interactively running the tests a much more pleasant
experience rather than something one dreads.  These tests will still
be run on the CI.  To run these manually run:

cargo test [TESTNAME] -- --ignored

ci/run.sh

@@ -33,6 +33,7 @@ else
     export CARGO_SUBCMD="test"
     export OPT="${OPT} "
     export OPT_RELEASE="${OPT_RELEASE} "
+    export OPT_RELEASE_IGNORED="${OPT_RELEASE} -- --ignored"
 fi
 
 # Run all the test configurations: