[Woo POS] Coupons: Disallow adding duplicate coupons to cart

[iamgabrielma]

Description

Partially addresses WOOMOB-259 by disallowing duplicated coupons to be added to the cart, while we get feedback from design on how to handle it UI-wise.

We also avoid calling the pos_coupon_added_to_cart track event multiple times by creating a new implementation for POSItemActionHandler, otherwise we could see the track event called multiple times despite the action being disallowed, as we used the same action handler across products and coupons:

🔵 Tracked pos_coupon_added_to_cart, properties: [blog_id: -1, is_wpcom_store: false, plan: , was_ecommerce_trial: false, site_url: https://indiemelon.mystagingwebsite.com, store_id: c5bd46cc-1804-4f7b-badb-bb98c449127f]
🔵 Tracked pos_coupon_added_to_cart, properties: [is_wpcom_store: false, plan: , store_id: c5bd46cc-1804-4f7b-badb-bb98c449127f, was_ecommerce_trial: false, blog_id: -1, site_url: https://indiemelon.mystagingwebsite.com]
🔵 Tracked pos_coupon_added_to_cart, properties: [site_url: https://indiemelon.mystagingwebsite.com, store_id: c5bd46cc-1804-4f7b-badb-bb98c449127f, plan: , is_wpcom_store: false, blog_id: -1, was_ecommerce_trial: false]

Testing information

• In POS, add a coupon to the cart
• Try again, observe how nothing happens. Removing it allows to be re-added.
• Confirm the pos_coupon_added_to_cart event is only logged once, when we add the coupon to the cart
• Confirm that adding products and variations to cart still work as expected.

Screenshots

Screen.Recording.2025-04-25.at.10.34.12.mov

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[wpmobilebot]

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

	App Name	WooCommerce iOS Prototype
	Build Number	29487
	Version	PR #15551
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	72e42f7
	Installation URL	3ajv3v99nksag

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[staskus]

@iamgabrielma thanks for the work!

Let's wait before merging until we get input from design. I think it's better right now to show an error in the checkout rather than not allow tapping the item without any visual signal.

Also, let's clarify if the item should be tappable when it's disabled (including the expired one). Maybe we wouldn't need a separate item handler logic.

Thanks!