rstest parametrizing for threading test cases (#582)

Changed tests to use the rstest #571. 
On my machine it makes the test (`--release`) run about 40% faster (2.8s
to 1.6s)

Places where the pattern was `let tests = [...]` with only one test
case, I changed to use rstest, since this makes adding more test cases
easier. I assumed that was the reason for the `tests` variable being
there despite there only being one test case.

Author: LWEdslev

Cargo.lock

@@ -46,6 +46,7 @@ sha3 = { version = "0.11.0-rc.2", default-features = false, features = ["oid"] }
 hex = { version = "0.4.3", features = ["serde"] }
 serde_json = "1.0.138"
 serde = { version = "1.0.184", features = ["derive"] }
+rstest = "0.26.1"
 
 [[bench]]
 name = "key"