feat(x-search-field): opt-in debounce for input events

[avanelsas]

Adds an opt-in debounce attribute (and reflected numeric property) to x-search-field. When set to a positive millisecond count, rapid typing coalesces into a single x-search-field-input event fired once the user pauses, carrying the field's final value. When the attribute is absent, 0, or invalid, the component keeps its current immediate per-keystroke behaviour, so the change is fully backwards compatible.

Only the outward x-search-field-input event is delayed. Local feedback — the clear button, form value, and validity — stays synchronous with each keystroke so the field never feels laggy. A pending debounced dispatch is cancelled when the field is cleared, the parent form is reset, or the element is disconnected, so a stale event never lands after the value is gone. The change, search, and clear events are never debounced.

The debounce timer id is stored via du/setv-untraced! as a transient, non-displayable handle (the documented pattern for opaque lifecycle handles), keeping the component stateless with no atom or volatile. Model parsing lives in a pure normalize-debounce. Covered by new model unit tests and integration tests for coalescing, cancel-on-clear, immediate-when-zero, and property reflection; docs and the demo gained a live debounce control with timestamped event logging. The framework adapter wrappers were regenerated to expose the new property.

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