support generating random CursorMove with arbitrary

fuzz/Cargo.toml

@@ -10,7 +10,7 @@ cargo-fuzz = true
 
 [dependencies]
 libfuzzer-sys = "0.4"
-arbitrary = "1"
+arbitrary = { version = "1", features = ["derive"] }
 tui-textarea = { path = "..", features = ["search", "arbitrary"] }
 tui-textarea-bench = { path = "../bench" }