Shipping Labels: Load settings and origin addresses synchronously only when data is not cached

[itsmeichigo]

Closes WOOMOB-627

Description

This PR continues the work in #15932 to improve the experience on the label purchase form:

• Fetches origin addresses and account settings from storage upon initialization.
• Updates weight unit and dimension units to use the injected shippingSettingsService.
• Fetches data from remote asynchronously when cached data are available.
• Add missing attributes for ShippingLabelAccountSettings to ensure that all data are stored properly.

Testing steps

1. Log out of the app to clear any cached data.
2. Log back in to a store with Woo Shipping set up.
3. Navigate to the Orders tab and open an order eligible for creating shipping labels.
4. Disconnect the Internet and tap the Create shipping label button.
5. Confirm that the loading state is displayed and then error state is displayed after requests time out.
6. Reconnect to the Internet and tap the reload button.
7. Confirm that data is loaded successfully and the purchase form is displayed.
8. Close the form and tap the Create shipping label button again.
9. Confirm that the purchase form is displayed immediately without the loading state.
10. Edit any Woo Shipping settings on the web (paper size, selected payment method, etc.) then repeat step 8. Confirm that the correct data is displayed after loading the purchase form.

Testing information

• Tested and confirmed with simulator iPhone 16 iOS 18.4.
• Updated migration tests and unit tests for the purchase form.

Screenshots

Simulator.Screen.Recording.-.iPhone.16.-.2025-07-22.at.16.39.52.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.

[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	pr15935-b5c2853
	Version	22.8
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	b5c2853
	Installation URL	2b5ouah9r0mko

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

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 22.9. 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.

Generated by 🚫 Danger

[RafaelKayumov]

LGTM. Tested, data loading/fetching works as described