Let the Escape key cancel completion popups

[rolandwalker]

Description

There is some lag as compared to canceling with control-g, due to the VT-100 limitation of representing Alt- keypresses as Escape- sequences.

Mentioned in #1009.

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 .

[scottnemes]

Verified escape key exits completions after a brief delay

[github-actions]

Summary: One potential regression around Alt- keybindings while the completion menu is open. No security concerns spotted.

Findings

1. Potential regression: Escape is bound with eager=True while completion is active. This will consume the leading Escape in Alt- sequences, so Alt-r and Alt-Enter will no longer work when the completion menu is open. Previously those bindings should have fired even with completions visible. Consider dropping eager=True, or handling Alt- sequences explicitly so they still work after canceling. File: mycli/key_bindings.py:70.

Missing tests or edge cases

1. No automated coverage for keybindings. If you keep the eager=True behavior, please add a test (or a small integration-style check) to assert expected behavior for Escape cancel and for Alt-r/Alt-Enter when completions are active, so the intended UX is locked in.

If you want, I can propose a concrete change to preserve Alt- bindings while still allowing Escape to cancel.