Settable ttimeoutlen for Escape key sequences

[rolandwalker]

Description

Since olden times, most terminals have sent Alt+key combinations, function keys, and so on as sequences of characters starting with Escape.

This creates an ambiguity. What if the user simply typed "Escape"? Terminal applications solve this by waiting some period of time before registering a plain "Escape". prompt_toolkit waits a default of 0.5 seconds.

This pause can be a nuisance for users who use the Escape key, especially users of vi keybindings.

Here we provide access to prompt_toolkit's ttimeoutlen property, making the value independent between Emacs and vi modes. At smaller values, an Escape key alone is recognized much more quickly. The toolbar UI for vi modes may still lag on the display of a change in state, but the keystroke is recognized for the typist.

This could also be used to improve the case of pressing Escape to cancel completions.

The setting is named after the Vim setting for familiarity to the group most likely to need it.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

Findings

1. Behavior regression: alternate F4 path does not apply the new timeout setting

   • In the normal F4 handler, toggling key mode updates event.app.ttimeoutlen, but the alternate sequence handler (Esc [ S) only flips editing_mode/key_bindings and leaves ttimeoutlen unchanged.
   • This makes behavior terminal-dependent and breaks the PR’s goal when F4 is emitted as an escape sequence.
   • Fix: mirror the ttimeoutlen assignment in the Esc [ S handler.
   • Reference: mycli/key_bindings.py:112, mycli/key_bindings.py:99

2. Missing regression test coverage for timeout switching

   • I don’t see tests validating that toggling Emacs/vi updates ttimeoutlen in both keybinding paths (F4 and Esc [ S), or that startup initializes mode-specific timeout.
   • Add tests around keybinding toggle behavior to prevent this regression from recurring.
   • Reference: mycli/key_bindings.py:99, mycli/main.py:1316

No direct security issues found in this diff.