Panic when completion menu items contains UTF-8 characters and (

[petricavalry]

Platform Arch Linux
Terminal software Alacritty

Same as title. nushell/nushell#13951 caused by this issues.

Thanks for all amazing work in reedline.

Steps to reproduce

1. Run the example completions with following lines changed.

   let commands = vec![
       "おはよう".into(),
       "おはよう(".into(),
   ];

2. Enter おは and press Tab.

Screenshots/Screencaptures

thread 'main' panicked at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/str/mod.rs:659:21:
byte index 4 is not a char boundary; it is inside 'は' (bytes 3..6) of `おはよう`
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::str::slice_error_fail_rt
   3: core::str::slice_error_fail
   4: core::str::<impl str>::split_at
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/str/mod.rs:659:21
   5: reedline::menu::columnar_menu::ColumnarMenu::create_string
             at ./src/menu/columnar_menu.rs:305:46
   6: <reedline::menu::columnar_menu::ColumnarMenu as reedline::menu::Menu>::menu_string::{{closure}}
             at ./src/menu/columnar_menu.rs:659:21
   7: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/ops/function.rs:305:13
   8: core::option::Option<T>::map
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/option.rs:1110:29
   9: <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/iter/adapters/map.rs:108:26
   10: <alloc::string::String as core::iter::traits::collect::FromIterator<alloc::string::String>>::from_iter
             at /usr/src/debug/rust/rustc-1.81.0-src/library/alloc/src/string.rs:2153:15
   11: core::iter::traits::iterator::Iterator::collect
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/iter/traits/iterator.rs:2005:9
   12: <reedline::menu::columnar_menu::ColumnarMenu as reedline::menu::Menu>::menu_string
             at ./src/menu/columnar_menu.rs:648:13
   13: <reedline::menu::ReedlineMenu as reedline::menu::Menu>::menu_string
             at ./src/menu/mod.rs:457:9
   14: reedline::painting::painter::Painter::print_menu
             at ./src/painting/painter.rs:307:27
   15: reedline::painting::painter::Painter::print_small_buffer
             at ./src/painting/painter.rs:359:13
   16: reedline::painting::painter::Painter::repaint_buffer
             at ./src/painting/painter.rs:234:13
   17: reedline::engine::Reedline::buffer_paint
             at ./src/engine.rs:1812:9
   18: reedline::engine::Reedline::repaint
             at ./src/engine.rs:1514:13
   19: reedline::engine::Reedline::read_line_helper
             at ./src/engine.rs:802:29
   20: reedline::engine::Reedline::read_line
             at ./src/engine.rs:646:22
   21: completions::main
             at ./examples/completions.rs:66:19
   22: core::ops::function::FnOnce::call_once
             at /usr/src/debug/rust/rustc-1.81.0-src/library/core/src/ops/function.rs:250:5