add benchmark to insert lines randomly

bench/Cargo.toml

@@ -14,6 +14,7 @@ tui = { version = "0.18", default-features = false }
 
 [dev-dependencies]
 criterion = "0.3"
+rand = { version = "0.8.5", features = ["small_rng"] }
 
 [[bench]]
 name = "insert"