scrollend event firing too early when user stops scrolling but keeps finger/trackpad contact

### Description

When a user scrolls using a **touchscreen** or **trackpad**, the polyfill dispatches a `scrollend` event **as soon as the scroll position stops changing**, even if the user’s finger or trackpad gesture is **still active**.

In contrast, the **native `scrollend` event** in Chrome and Firefox fires **after** the scroll gesture fully completes — that is, when the user lifts their finger or ends the input sequence (including momentum scrolling).

This results in the polyfill reporting a “scroll end” too early, while the user is still in control of the gesture.

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### 🧩 Steps to Reproduce

1. Use the Scrollyfills polyfill on Safari (or another browser without native `scrollend`).
2. Add a listener:

```js
window.addEventListener('scrollend', () => console.log('scrollend fired'));
```

3. Scroll a container (or the page) using:
- a **trackpad**, or
- a **touchscreen**.
4. Stop movement briefly but **keep your finger or trackpad contact active** — don’t release yet.

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### ❌ Actual Behavior

- The polyfill dispatches `scrollend` immediately after scroll motion stops, **even though the gesture is still active**.
- If the user then resumes scrolling without lifting their finger, multiple premature `scrollend` events may fire within the same gesture.

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### ✅ Expected Behavior

- `scrollend` should fire **only after the user has finished the gesture**, i.e. after:
- the final scroll motion has stopped **and**
- the finger or trackpad contact has ended (`touchend` / `mouseup`).
- The event should also fire once **inertial (momentum) scrolling** ends.

This matches native `scrollend` behavior in Chrome/Firefox.

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### 💡 Notes / Ideas

- The polyfill currently seems to rely solely on scroll position stability to infer “scroll end.”
- It should consider combining that with gesture-end events (`touchend`, `mouseup`) to ensure the user has actually released the scroll interaction.
- Chrome’s native implementation delays `scrollend` until the full scroll transaction (including momentum) is over.

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### 🧰 Environment

- **Browser:** Safari 26.0.1 (macOS)
- **Polyfill:** Scrollyfills v1.0.4
- **Device:** MacBook trackpad

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### 🧠 Why this matters

Without this distinction, scroll-driven UIs (e.g., scroll snapping or scroll-triggered animations) may re-enable snapping or trigger transitions **while the user is still interacting**, resulting in janky or conflicting UX compared to browsers with native `scrollend`.

Reproduce the issue in Scrollyfills v1.0.4 on Safari with a trackpad or touchscreen, then locate the scrollend polyfill entry point that infers completion from scroll-position stability. Verify the behavior against the reported gesture sequence, including pauses, resumed movement, touchend or mouseup, and momentum scrolling; done means one event fires only after the full gesture ends.

Written by the indexing model from the issue text.