Speed up timestamp generation when logging (#9933)

* Speed up timestamp generation when logging

* Align to review comments.

* Correct a typo

substrate/client/tracing/Cargo.toml

@@ -15,6 +15,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 [dependencies]
 ansi_term = "0.12.1"
 atty = "0.2.13"
+chrono = "0.4.19"
 lazy_static = "1.4.0"
 log = { version = "0.4.8" }
 once_cell = "1.4.1"
@@ -35,3 +36,10 @@ sp-core = { version = "4.0.0-dev", path = "../../primitives/core" }
 sc-client-api = { version = "4.0.0-dev", path = "../api" }
 sc-tracing-proc-macro = { version = "4.0.0-dev", path = "./proc-macro" }
 sc-rpc-server = { version = "4.0.0-dev", path = "../rpc-servers" }
+
+[dev-dependencies]
+criterion = "0.3"
+
+[[bench]]
+name = "bench"
+harness = false