[Shipping labels] Load the shipping services and rates from remote in the UI layer

Description

This adds support for loading the shipping label rates from remote in the Woo Shipping label flow. New behavior:

When the shipping service section appears, it shows a loading indicator to show that the rates are being loaded.
After the rates are loaded, the list of actual rates for the label are displayed.

Note that viewing the shipping service section still requires (for now) testing code to set the selected package.

WooShippingServiceViewModel now makes a remote request to load the label rates when it is initialized:
- The init method now takes the required parameters for the remote request, and sets the loading state with placeholder values.
- The init method also calls a new method to make the remote request. After receiving the response, it updates the available rates, regenerates the service tabs and rates, and sets the loading state.
WooShippingServiceView now shows a shimmering, redacted placeholder view while the rates are loading.
WooShippingCreateLabelsViewModel is updated to set the shipping service view model after a package is selected. This introduces a selectedPackage property we can set in the package selection flow.
Updates unit tests. ShippingLabelPackageSelected is now copiable for ease of unit testing.

Prerequisite: The Woo Shipping extension installed and activated, with at least one order with the processing status and a physical product.

Update WooShippingCreateLabelsViewModel to provide a value for selectedPackage that can be used in the remote request.
Build and run the app with the revampedShippingLabelCreation feature flag enabled.
Go to the Orders tab.
Select an order eligible for a shipping label.
Tap "Create Shipping Label."
Confirm the Shipping service section is displayed with a loading view.
Once the request is completed, confirm a list of shipping rates is displayed, and you can sort and select the rates as expected.
Confirm that selecting a rate updates the shipment costs section in the "Shipment details" bottom sheet as expected.

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

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

[x] 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.
[x] Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
[x] 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.

	App Name	WooCommerce iOS
	Build Number	pr14412-5756d86
	Version	21.1
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	5756d86bb926060977e52e62cac74eee71beb228
	App Center Build	WooCommerce - Prototype Builds #11586