Enable parallel tests to reduce test time (#4919)

* Add crate to serialize some tests

* Ignore unused attribute warning

* Enable parallel run in CI

* Try to fix lograte tests

* Fix interdependent counter tests

scripts/coverage.sh

@@ -36,7 +36,7 @@ rm -rf target/cov/$reportName
 
 source ci/rust-version.sh nightly
 _ cargo +$rust_nightly build --target-dir target/cov "$crate"
-_ cargo +$rust_nightly test --target-dir target/cov --lib "$crate" -- --test-threads=1
+_ cargo +$rust_nightly test --target-dir target/cov --lib "$crate"
 
 echo "--- grcov"