[Woo POS] [Variable Products] Only show one ghost cell for next page

[joshheald]

Closes: #14955

Description

This PR changes the loading next page UI for products and variations to match Android.

We now show only one ghost cell when loading the next page, but continue to show 8 when loading the first page of variations.

Steps to reproduce

1. Launch the app and open POS
2. Observe that the initial loading state is a spinner.
3. Scroll to the end of the product list; observe that one ghost cell is shown while loading new items.
4. Open a variation; observe that the loading state is a page of ghost cells which all animate.
5. Scroll to the end of the list (min 26 variations); observe that the loading state for the next page is one ghost cell.

Testing information

Screenshots

ghost.cell.updates.mp4

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

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• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 21.5. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr14956-a3b15eb
	Version	21.4
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	a3b15eb
	App Center Build	WooCommerce - Prototype Builds #12660

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[staskus]

I can confirm that only one ghost cell is visible when scrolling to the next page. 👍