Expand benchmarks

* Add benchmarks for basic ops (add, sub, mul, div, etc.) for the
  decimal types.
* Use seeded rng for reproducible results.
* Use a longer measurement period for more consistant results.

Author: jean-airoldie

dec/Cargo.toml

@@ -19,7 +19,9 @@ static_assertions = "1.1.0"
 
 [dev-dependencies]
 criterion = "0.3.0"
-rand = "0.7.3"
+itertools = "0.10.1"
+rand = "0.8.4"
+rand_xoshiro = "0.6.0"
 serde_test = "1.0.117"
 
 [package.metadata.docs.rs]