add arbitrary crate as optional dependency

to avoid converting `Input` in fuzz test for making arbitrary inputs

Cargo.toml

@@ -31,6 +31,7 @@ crossterm = { version = "0.23", optional = true }
 regex = { version = "1", optional = true }
 termion = { version = "1.5", optional = true }
 tui = { version = "0.18", default-features = false }
+arbitrary = { version = "1", features = ["derive"], optional = true }
 
 [[example]]
 name = "minimal"