[SergioRibera]

Description

Adds the touch model of native text fields to freya-edit, without any UI:

• TouchEditEvent (down, move, up, long press, handle down...) processed with UseEditable::process_touch, and TouchSelection, the touch state read with UseEditable::touch.
• A tap places the cursor when the finger lifts, unless it moved further than TOUCH_SLOP (then it was a scroll). A double tap selects a word with touch timing and distance, a long press selects the word under the finger and dragging then extends it word by word, and the selection handles move each end.
• LONG_PRESS_TIMEOUT and TOUCH_SLOP are public so the owner runs the timer and the checks.

It's a separate event type rather than new EditableEvent variants, so code matching on EditableEvent (like freya-code-editor) keeps compiling.

Motivation

Editing text with a finger follows the mouse model today: the cursor moves as soon as the finger goes down and dragging selects. This is the base Input (and custom editors built on use_editable) need to behave like EditText / Compose /Flutter fields.

Checklist

• I have tested my changes.
• I used AI assistance (e.g. ChatGPT, Copilot, etc.) to write this code.
• I have added or updated documentation where relevant.
• I have added or updated tests where relevant.