Add option to delete whole words when holding the delete key

[4di-hello]

When enabled, holding the delete key switches from deleting characters to deleting whole words after a moment, getting faster the longer it is held.

• Two sliders: speed (start interval) and acceleration, both with a "Recommended" step
• One haptic/audio feedback per deleted word instead of per key repeat
• Not used for languages without spaces (a "word" could be a whole sentence there)
• Works in web editors (sends DEL key events there)
• Off by default
• Unit tests for word boundaries, intervals and the held-key behaviour
• Tested for several days on a Xiaomi 14T Pro (HyperOS)

[LeanBitLab]

Thank you for the clean implementation and unit test coverage!

Word deletion on held backspace is a convenient feature, but in its current form, adding two separate preference sliders (start interval and acceleration) introduces significant settings clutter.

As part of our project focus to prevent settings bloat, we prefer sensible, well-tuned defaults rather than exposing granular configuration sliders to the user. Would you be open to simplifying this to a single toggle with fixed, optimal timing curves (no extra sliders)?

[4di-hello]

Done: simplified to a single toggle with a fixed timing curve, the speed and acceleration sliders are removed.