Make ratatui dependency optional

Author: sayanarijit

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tui-input"
-version = "0.12.0"
+version = "0.12.1"
 edition = "2021"
 authors = ["Arijit Basu <hi@arijitbasu.in>"]
 description = "TUI input library supporting multiple backends"
@@ -22,7 +22,9 @@ unicode-width = "0.2.0"
 serde = { version = "1.0.218", optional = true, features = ["derive"] }
 crossterm = { version = "0.29.0", optional = true }
 termion = { version = "4.0.4", optional = true }
-ratatui = { version = "0.30.0-alpha.2", features = ["crossterm"] }
+ratatui = { version = "0.30.0-alpha.2", optional = true, features = [
+  "crossterm",
+] }
 
 [dev-dependencies]