chore(fuzz): upgrade targets, fix false positives, and add invariant assertions (#11)

- Fix insert_delete target using .unwrap() causing false-positive crashes
  on arbitrary::Error (input exhaustion)
- Fix fuzz Cargo.toml referencing wrong package name (tui-textarea vs
  tui-textarea-2)
- Add invariant assertions (cursor bounds, lines non-empty, selection
  validity) to all targets
- Add 4 new fuzz targets: undo_redo, selection, wrap_render, search
- Expand existing targets with full delete/insert variant coverage,
  input_without_shortcuts, set_yank_text, set_max_histories, and clear
- Add DummyBackend::resize() for variable-width wrap rendering tests

fuzz/fuzz_targets/wrap_render.rs

@@ -0,0 +1,55 @@
+#![no_main]
+
+use arbitrary::{Arbitrary, Result, Unstructured};
+use libfuzzer_sys::fuzz_target;
+use tui_textarea::{CursorMove, TextArea, WrapMode};
+use tui_textarea_bench::{dummy_terminal, TerminalExt};
+
+fn assert_invariants(textarea: &TextArea<'_>) {
+    let lines = textarea.lines();
+    assert!(!lines.is_empty(), "lines must never be empty");
+    let (row, col) = textarea.cursor();
+    assert!(
+        row < lines.len(),
+        "cursor row {row} out of bounds (lines: {})",
+        lines.len()
+    );
+    assert!(
+        col <= lines[row].chars().count(),
+        "cursor col {col} out of bounds (line {row} chars: {})",
+        lines[row].chars().count(),
+    );
+}
+
+fn fuzz(data: &[u8]) -> Result<()> {
+    let mut term = dummy_terminal();
+    let mut data = Unstructured::new(data);
+
+    let text = <&str>::arbitrary(&mut data)?;
+    let wrap_mode = WrapMode::arbitrary(&mut data)?;
+    let width: u16 = *data.choose(&[1, 4, 10, 40, 80, 200])?;
+
+    term.backend_mut().resize(width, 12);
+
+    let mut textarea = TextArea::from(text.lines());
+    textarea.set_wrap_mode(wrap_mode);
+
+    for _ in 0..100 {
+        let m = CursorMove::arbitrary(&mut data)?;
+        textarea.move_cursor(m);
+        term.draw_textarea(&textarea);
+        assert_invariants(&textarea);
+
+        if bool::arbitrary(&mut data)? {
+            let s = <&str>::arbitrary(&mut data)?;
+            textarea.insert_str(s);
+            term.draw_textarea(&textarea);
+            assert_invariants(&textarea);
+        }
+    }
+    Ok(())
+}
+
+fuzz_target!(|data: &[u8]| {
+    let _ = fuzz(data);
+});